Google announced that it will not be treating the
rel="nofollow" attribute as a signal any more, but as a hint. The background is that so many CMS’es are designating every link as nofollow.
They’re introducing two new hints:
ugc for user generated content and
sponsored for paid links.
For the UGC, they’re explicitly mentioning forums.
My opinion is that this is a big step forward, since the vast use of nofollow was killing the idea behind PageRank.