This is just a terrific idea.  Anyone who codes can attest to how useful stack overflow is.  I don't really know if it's the details of their approach or just some kind of cultural convergence, but there's no question this model can be hugely successful, and it would be great to extend it to neuroimaging.  I do agree that language agnosticism is important, but perhaps more important would be getting commitments from a bunch of knowledgeable people to check in once or twice a week.  I've looked at some of the less populated stackexchange sites, and it seems like there's a bit of a chicken/egg problem in attracting users to a site before it's very comprehensive.  Maybe it would also be useful to seed it with a bunch of easily answered or at least important questions, so that it would be useful right away.  (I'd be more than happy to help with this, although I almost invariably fall in with the minority view.)

I imagine the best place for this would be someplace that's already a community hub, like NITRC.  But in the unlikely event no one more centrally located takes this up, I'd be happy to set it up on our center's server.

dan