Username spoofing on the wiki may also be covered by the libel laws of your country. If your name is attributed to comments and those comments harm your professional reputation. Libel cases tend to be very difficult to prosecute as damages are hard to prove (you will typically need such evidence as an employer who has cited the comment as one of the reasons for refusing to employ you).
Courts tend not to consider such cases seriously due to the large number of internet sites and the relatively low level of users on most sites. The rationale generally used by the courts is that the contents of the Internet are ephemeral and very volatile therefore libelous comments only have to be removed and the problem is solved. Further action may however still be possible if there is evidence that a persons reputation has been harmed. However such action is civil, not criminal, and evidence of harm to reputation is fairly hard to acquire.
In general, libel cases never reach the courts due to compliance by webmasters.
In France, the webmaster is asked to remove the offensive comments and if he doesn't the court forces him to. Damages are not attributed.
[In the US, a number of companies have brought civil actions against individuals, alleging that comments made in chat rooms, guest books, bulletin boards, and similar forums are libelous. The US legal system is still evolving a response to the dilemma posed by search engines. The difficulty is that the offending text can remain available online via cached search engine records, copies on other sites, and so on, libeling the target, for an arbitrary period after being removed at the source.]
In the UK, there was an (in)famous case of libel: http://news.bbc.co.uk/1/hi/sci/tech/695596.stm