All user generated content should use rel=nofollow tag and that includes member profile user "homepage" links.
Guys, the whole point of this thread was to discuss an issue of having URLs in the text of a UGC page but not as links, nofollow or do follow. Just plain text. Also, I have no user profile pages. So, there should technically be no reason to spam my forum because you cannot gather links from it but I assume that spammers can only survive it they automate their operations. I doubt anyone spamming there has actually been to any of my sites to verify if it merits spamming.
In any case, since the forums are doing very poorly in Google in the last two weeks, I am trying to find out if this "lite" version of parasitic hosting might have contributed to the drastic reduction in Google rankings. I think the consensus from this thread is that it was probably not the reason for the penalty.
I do not advocate leaving your forums unattended if you disable URL into links conversion. I was merely suggesting that no matter how you try there will always be some URLs posted that you'd rather not to link to or even mention and so it would be important to know the implications.