A Hamburg court have ruled that forum owners are liable for what goes on in their forums:
http://www.heise.de/english/newsticker/news/72085
I am not sure whether similar rulings has been made in other countries, but I could think that there is something similar in effect in the US, however it is speculations.
I do not know of any such ruling in Denmark (yet), however there have been somewhat related cases where providers of chat-services have been ruled to more actively moderate what happens on the site due to the site being used to organise beatings of school-kids by school-kids (amongst other things)
Thoughts?
Personally - I'm a bit torn about this, because I can see both the pros and cons (maybe because I'm both moderator and user at this site). I fully see the reasons for keeping strict rules as to what is allowed and not allowed, however, I do not hope the cup will flow over and we can't debate for instance actions of companies etc withouth holding (in GB's case) Buck liable, if the company in question disagreered with the opinions posted and thought them slander or such.