I think it was when talking to Jonathan from Plagiarism Today (http://www.plagiarismtoday.com) that I was told that forum posts should be regarded as the authors' own, legal copyright property. I may have some old notes on this around that I can dig up.

Some forums (and sites like YouTube) write some Terms of Use/EULAs to waive their content rights to the site owners (not for any nefarious reasons), although I doubt that these "agreements" hold up.

If I had any comments or forum posts that were copied verbatim in a manner that upset me, I would definitely pursue it legally. But I'm a fanatic like that.