Don't forget that some forum threads (on high PR forums) will rank well in Google searches and you can get traffic from them. That's the major benefit to doing a lot of good posts on the same forum.
I posted a fantastic piece of software on this forum for getting hundreds of quality white hat links including many ranked 8. That was until some jealous f+++++ got envious and it was removed for spam. I posted it on another forum and sold 25 copies in one night.
But the "nofollow" category is sth that applies to the whole page or just to the link? Because, looking in a specific forum I have found somoe nofollow but not of the in my link...digital points is no or do follow?