I also went to a Nanowrimo (why did I include that link like everyone hasn't heard of Nanowrimo?) gathering last night and it was fun, although slightly deceptive since neither I, nor any of the members of my writing group, are participating. I've finished two Nanowrimii, in 2002 and 2003, and the outcome of both of those novels has sort of taken the shine out of the concept for me. The first novel, I didn't do anything with, and don't think I even have a file of it anymore. I remember it was post-apocalyptic, but that's it. The second one became my thesis novel, and basically the entire thing was scrapped and rewritten (and I'm not really fond of it anymore either, now). I got entirely no usable writing out of either one of those excursions.
And this would be okay, if not for the fact that I can't abide having writing that doesn't "count." In college, I struggled a ton with writing exercises, and sometimes wouldn't even turn them in because I found them so, so difficult. Things like character sketches, constrained writing, etc., would all have to be bent into the service of a story suitable for potential publication, and this was true even before I attempted to publish anything. I guess this is probably because I don't think of the act of writing itself as fun. (Another blog post for another time!)
So, good luck on your Nanowrimo novels, everyone who's doing it! But this year, as with the last seven, I will be bowing out.