Steven Riddle, the principal of Leverette Junior High School, filed a defamation lawsuit against Chris Myers, the operator of SwampBubbles, a website that describes itself as " a user centered site dedicated to breaking news and political discussion of Toledo and Northwest Ohio," claiming that the site has been posting items that are "false and defamatory."

According to the complaint, defamatory postings were written by at least three unnamed people in response to a story on the site about a Leverette school employee charged with sexually assaulting a student. 

Riddle also named as a defendant "Another Leverette Teacher," which the complaint did not name.  According to the ToledoBlade.com, the complaint also requested that Myers be ordered to provide facts that would allow Riddle "to identify the persons who defamed him."

Update:

On March 3, 2008, Meyers filed a Motion For Protective Order and in the Alternative, Motion For Summary Judgment.

On September 23, 2008, the court scheduled an oral hearing on Myers' Motion for Protective Order and in the Alternative, Motion for Summary Judgment for October 30, 2008 at 11:00 a.m.

On November 14, 2008, plaintiff filed a notice of dismissal without prejudice which the Court granted.

Tim Puntarelli, Dean of Roncalli High Scool in Indianapolis, filed a defamation lawsuit against an anonymous Facebook user (or users) who allegedly created a fake profie for him and used it to send inappropriate messages to students.  According to one press report, the lawsuit also claimed that the user engaged in harassment and identity theft.  Puntarelli sought information about the anonymous user or users from Facebook, which resisted this effort. 

The court ultimately ordered Facebook to produce identifying information for its user(s). Facebook removed the profile at Puntarelli's request before the lawsuit was filed.

IT Service Management Forum USA (ITSMF), a nonprofit organization supporting IT professionals, filed a defamation lawsuit against its former executive director, James Prunty, alleging that he attempted to discredit the organization by posting comments on the IT Skeptic blog under the fictitious name "Julie M. Linden, Ph.D."

According to an article in Computerworld, ITSMF filed defamation and breach of fiduciary duty claims in California state court based on comments made by "Julie Linden" that accused ITSMF of rigging its online election of board members. The comments also impugned the integrity of the organization and suggested that people should distance themselves from it.

ITSMF initial filed its complaint against Linden, and on January 7, 2008 sought an ex parte order from the court granting it permission to conduct expedited discovery in the case.  The court granted ITSMF's request that same day. Apparently as a result of that discovery, ITSMF filed an amended complaint on June 4, 2008, adding Prunty as a defendant.

Bronx District Attorney Robert T. Johnson issued a grand jury subpoena to New York political blog Room Eight seeking identifying information for several anonymous bloggers and commentors. The subpoena ordered Room Eight operators Gur Tsabar and Ben Smith not to disclose the subpoena's existence -- not even to the anonymous posters -- because doing so could "impede the investigation" and "interfere with law enforcement."

In the disputed posts, Room Eight posters using the pseudonyms "Republican Dissident" (RD), "Dissident Hunter," and "Anonymous" criticized local politicians and Bronx Republican Party officials. According to copies of posts attached to the subpoena, a poster accused Bronx Board of Elections Commissioner J.C. Polanco and board employee Dawn Sandow of having an extramarital affair and other posters accused them of committing misdeeds. Many of the posts focused on Sandow, including one that included a graphic of a witch flying on a broom and told her to "HAVE A NICE FLIGHT" (caps in the original). Other postings attached to the subpoena alleged that Bronx Republican Party official Jay Savino and other local politicians and officials had engaged in fraudulent and illegal activities.

According to Room Eight's court filings, anonymous poster "Republican Dissident" also criticized the Bronx Republican Party for failing to run candidates against District Attorney Johnson, the D.A. who issued the subpoena to Room Eight. However, the District Attorney did not include these posts when he sent the subpoena requesting the information from Room Eight.

Following receipt of the subpoena, Tsabar and Smith sought permission from the D.A.'s Office to notify the anonymous posters about the subpoena so they could object to the revelation of their identifying information. Negotiations between the parties failed, so the non-disclosure demand remained in force.

On May 22, 2008, Tsabar and Smith moved to quash the subpoena in the Supreme Court of New York for Bronx County. They argued that the subpoena threatened the posters' First Amendment right to speak anonymously, analogizing to numerous civil cases protecting online anonymity rights in the context of subpoenas. According to Public Citizen, counsel for Tsabar and Smith, Room Eight also threatened to file a federal suit on the ground that the threat of criminal prosection violated the posters' right to criticized the District Attorney.

After Room Eight filed its motion to quash, Johnson withdrew the subpoena. Public Citizen advised the D.A. that it still would file suit if he intended that the subpoena's non-disclosure language remain in force. The D.A. then freed the defendants to disclose information regarding the subpoenas.

On June 10, 2008, the Associated Press ("AP") sent a takedown request under the Digital Millennium Copyright Act to Rogers Cadenhead, the founder of Drudge Retort, a liberal alternative to (and parody of) the well-known Drudge Report, demanding that he remove six user-submitted blog entries and one user comment on the site that contained quotations from AP articles.  

The Drudge Retort is a community site similar to Digg and Reddit, allowing its users to contribute blog entries, comments, and links to interesting news articles. According to Cadenhead, none of the six posts republished the full text of an AP story; instead, each contained quotes ranging in length from 33 to 79 words (although the posts have been removed, Cadenhead has provided a summary of them here).

Please note that contrary to your assertion, AP considers that the Drudge Retort users' use of AP content does not fall within the parameters of fair use. The use is not fair use simply because the work copied happened to be a news article and that the use is of the headline and the first few sentences only. This is a misunderstanding of the doctrine of "fair use." AP considers taking the headline and lede of a story without a proper license to be an infringement of its copyrights, and additionally constitutes "hot news" misappropriation.

It doesn't appear that AP is continuing to pursue a "hot news" misappropriation claim against Drudge Retort.  This little known legal doctrine, which saw its genesis in 1918 in International News Service v. Associated Press, 248 U.S. 215 (1918), seems to have fallen out of favor because the 1976 Copyright Act preempts all legal and equitable rights that are equivalent to the exclusive rights offered by federal copyright law. As a result, in National Basketball Ass'n v. Motorola, 105 F.3d 841, 844 (1997), one of the few cases to address a "hot news" claim, the Second Circuit set an exceptionally high standard for such claims to be viable, requiring, among other things, that the information be time-sensitive; the defendant be in direct competition with the plaintiff; and the continued publishing of the "hot news" would so reduce the plaintiff's incentive to produce the product or service that its existence or quality would be substantially threatened.

On June 16, 2008, the New York Times reported that AP was reconsidering its request while it creates a set of guidelines for bloggers and websites that excerpt AP material.

Update:

On June 20, 2008, Cadenhead and AP announced that they had settled their copyright dispute.  As of June 23, the six posts remain inaccessible.

Anonymous users posted negative comments about Matrixx Initiatives on the Yahoo! Finance and Silicon Investor message boards. Matrixx filed a lawsuit against the anonymous "John Doe" posters in an Arizona court alleging defamation and other claims. Matrixx received information from Yahoo! that some of the postings could be traced to computers owned by Barbary Coast Capital Management, LLC, a San Francisco hedge fund. Matrixx got permission from the Arizona court to take a deposition in California of Stephen Worthington, a manager at Barbary Coast. During the deposition, counsel for Matrixx asked Worthington about the identity of the anonymous posters, and he refused to reveal their identity or to say whether he was one of them. Matrixx obtained an order from the Santa Clara Superior Court in California requiring Worthington to answer the questions.

Barbary Coast and Worthington appealed the trial court's decision, claiming that it violated the posters' First Amendment right to speak anonymously. The appellate court affirmed the decision of the trial court, holding that Barbary Coast and Worthington lacked the standing to assert the First Amendment rights of the anonymous posters.

Amy Ancel, a local politician in Connecticut, posted a comment on WestportNow.com, a community news site in Westport Connecticut, in which she accused two users of the site of libeling her. The disputed comments occurred in a series of comments relating to the relocation of a local YMCA in which two users of the site, Adrian Bowles and Ronald Wimer, criticized her and questioned Ancel's placement of signs opposing her political opponent.

In a March 5, 2008 comment on the site, Ancel wrote:

[C]onsider this my notice to you and Mr. Wimer to cease and desist libeling me in this website, the newspapers, the Water Rats Parents’ Club website “Mahackeno Now,” Politicus Machamux and any other publications you and Mr. Wimer author or have access to. My next notice will come from my attorneys.

As of June 16, 2009, it appears that no action has been taken by any of the parties.

On December 10, 2007, an investigator with the Kansas University Office of Public Safety delivered a search warrant to the Lawrence Journal-World, a highly regarded newspaper in Lawrence, Kansas, demanding access to the newspaper’s computer servers. The search warrant, issued by Douglas County District Judge Stephen Six, sought information about the identity of an individual who had posted anonymous comments on the newspaper's website, LJWorld.com.

Investigators were seeking the identity of a user who had posted comments on the paper's website under the screen name "a2thek." The pseudonymous user had commented on an article about a Kansas University student who was found dead in a KU dorm room, indicating that the death was heroin-related.

According to the Lawrence World-Journal, the investigator left before executing the warrant:

When presented with the search warrant, the newspaper was given the opportunity to call its attorney [Bernard Rhodes], who contacted the district attorney’s office and the court to object to the search warrant. During that time period, the KU investigator left the Journal-World offices without executing the search warrant and did not return.

Rhodes stated that he believed the search warrant was issued contrary to the federal Privacy Protection Act, which restricts the ability of law enforcement to conduct searches of news-gathering organizations.

On January 6, 2008, after the paper made the search warrant public, a2thek posted a follow-up comment apologizing for providing inaccurate information in his earlier comment:

This infomation [sic] is not 100% correct and I would like to take some time to apologize for any mis-information. The guy that works with me I overheard in the bathrool [sic] making this speculation of what actually happened so I dont [sic] know if it's actual fact or hearsay. I do once again dont [sic] want to draw any lines or conclusions being I really dont know anything about all of it and I think the guy at work was just an aquitance [sic] and went to school with the guy and that's what he heard. I guess when a autopsy is performed that will get you the answers that your looking for. Sorry for all the misleading info once again.

Sorenson's Ranch School, a rehabilitation center and school for troubled youths in Koosharem, Utah, along with two of its officers filed a defamation lawsuit against MySpace and 10 unknown John Doe defendants claiming that a MySpace page had been set up in which users criticized the school's operations (the page no longer exists).

In the suit, the school alleged that MySpace and some anonymous users published statements falsely indicating that the Sorensons engaged in child abuse, employed underqualified staff, and engaged in false advertising. The plaintiffs also claimed that the defendants used "vulgar and inappropriate language" and otherwise made defamatory statements regarding the school.

The complaint asked for $125,000 in damages and an injunction against further publication of the defamatory comments.

There is no indication in the case docket that plaintiffs served MySpace with the complaint, and no defendant filed an answer. About four months after filing the complaint, with no further filings or motions occuring in the case, the plaintiffs filed a notice of voluntary dismissal.