Many things improve search engine ranking
On the other hand, forum members can also be. How to say this politely? Flaming morons. How to you work out which forums and which forum members are worth reading? It comes down to reading a wide selection of forums and noting patterns over time. Seeing whether an official speaker for a given search engine is a member of the forum is a good idea as well. While an official speaker isn't a stamp of trustworthiness, his or her presence does mean that the forum is influential enough for the search engine to take note.