Here's an interesting piece of technical law: you can't sue Wikipedia for what is said about you on the sire, as Fuzzy Zoeller had found out:
The offending paragraphs allegedly slandering Zoeller’s name were posted on December 20 2006, and have now been removed, but not before they were discovered, with Fuzzy Zoeller being named as ‘John Doe’ in the legal action that has subsequently been initiated to clear his name.
The IP address of the posts was traced back to education consulting firm Josef Silny & Associates of Miami, although Mr Silny says he is surprised that the complaint originated from his computer systems and doesn’t know who at his company might have made the offending Wikipedia posts.
Wikipedia is the encyclopedia that anyone can edit, although following previous instances where Wikipedia entries were defaced and edited with potentially defamatory information, with people previously affected by inaccurate Wikipedia entries including John Seigenthaler, a former assistant to Robert Kennedy, who was falsely accused of being a suspected participant in the assassinations of the Kennedy brothers, along with US politicians who have had their Wikipedia entries besmirched.
The thing is, it doesn't explain why you can't sue Wikipedia. Is it because they're like a common carrier?