As an interesting aside, everyone's favorite organic encyclopedic network, Wikipedia, was cleared by the French Courts of libel on Monday on the grounds that the organization is not responsible for the content posted upon its networks by its users. Here's the original detailed article in LeMonde (French), and another brief summary that's been picked up by the American press.
The three plaintiffs in the case claimed that by allowing their sexual orientations to be revealed in an article (which connected them to national gay activist movements), Wikipedia had participated in (or at least facilitated) a sort of editorial defamation and violation of their individual privacies. The Judges ruled that since Wikipedia is a "benevolent construction... [which] exercises no control over the contents of its articles," it isn't held to the same editorial responsibility as are traditional print publications.
The article also notes the importance of the decision before the next municipal elections, since it upholds the right of individuals to post information relating to the candidates on the Wikipedia network. Vive l'E-Citizenship, eh?
Of course, IP addresses are also logged on the site, so the Plaintiff's available recourse is to track down the original posters... though the LeMonde article notes that given the rise of publicly accessible computers and wifi networks, anonymity is still fairly easy to achieve for wouldbe political wikiposters.