RCIX, having Toady redirect users from the forum allows them to find it, but doesn't address my main point: leaving the forum site. It is easy to be waiting on a community game post or a reply to something, and casually browse the help forum and maybe answer a question or two. It is harder to leave the forums (where you have the nice Show New Replies button and the ability to click back to your forum of interest in one click) and then answer a question or two and come back.
Beyond just inertia, I think a lot of the good support we have here comes from time killing, which will honestly never translate. Actually I think that has a bit to do with all the things that get discovered that people are then too "lazy" to post on the wiki. It isn't that they meant to and never got around to it so much as that it was an extra step in the thought process that they never really got to. Out of site, out of mind. (Pun intended).
Speaking as an occasional forum poster (I usually post only on the Gameplay Questions forum, helping out new users when I feel like it) I agree with UmbrageOfSnow. I use only three sites, the wiki, the forums, and the bug tracker when trying to answer my own questions, in that order. I like helping out new players, and I find the wiki far more useful than the forums for getting answers for my own gameplay problems.
Adding another site would create yet another smaller subset of users, both experienced and new, which will split the community. (In my opinion, far, far fewer people will go to the SE site, even if Toady removes the Gameplay Questions forum here). I for one will not use yet another site - I'm finding I'm not using the bug tracker as frequently as I should, because that requires a separate login.
Now, if the new SE thingamajig REPLACES the bay12forums (same site, same login, same front page) then I would reluctantly use it, because there won't be anywhere else to go for questions and answers. But that's the only way I see myself using this, despite how technologically/social-networkly/shiny advantageous SE is over this forum.