I know this isn't a direct answer to Anders' question. But he and I do have a similar interest in this site; and since this is the meta forum, perhaps posting this as an "answer" is acceptable.
I am the primary developer of CVX, a convex optimization modeling framework for MATLAB. It is similar to YALMIP, whose author participate in this forum. I too am convinced of the value of a discussion community for usage questions, as distinct from a standard bug-reporting service (which I also have). The StackExchange format seemed attractive as well, so I created the CVX Forum using an open-source StackExchange alternative.
Frankly, I have mixed feelings about my choice. On one hand, it is nice to be able to have complete control over the content, format, and so forth. On the other hand, because the site is so specialized, I don't have much participation on the answer side---I supply the bulk of the answers, although a couple of users have begun chiming in. I don't necessarily mind, but that's not much of a community. Furthermore, people don't make much use of the voting facility.
That may be due to the fact that people who are already comfortable with CVX aren't likely to hang around in a forum where there is nothing but support questions. What's nice about a more general forum like SciComp is that it that the diversity of topics and variety of expertise makes it an educational and enjoyable place to lurk, read, and occasionally answer. It might also be good for the questioners as well: to have a community where their questions are expected to be well-posed, complete, and clear.
The long-term solution for me, then, might be to encourage my users to ask their questions here and to phase out the CVX Forum. (Bug reports are another matter; I have a separate trouble ticket system for that.) I don't think that's something I would want to do until this site leaves beta, although that might create a sort of chicken-and-egg problem. Perhaps I should simply participate in both forums for the time being, and if Aron or Geoff would like to create a CVX tag, I can watch out for that.