How about "workshop"?
I agree about the kiddish vibe of "camp" and I also agree that "retreat" has a sort of religious hue to it as well. Some guy died on a "mysterious Buddhist retreat" recently.
I like workshop best of all the options presented so far.
The new Center for Applied Rationality website has launched! We'll be adding content as time goes by. Let us know if you find broken links, etc.