Wanted to point out that you can get a secure 10x12 private workspace with wired internet and a window for about $400 at Activspace in the Mission. It's a new building with stuff like an internal courtyard with BBQ grills. The building caters to artists but when I looked at a space it seemed like a good percentage of people did things like flash development.
Sam didn't review http://hackerdojo.pbwiki.com yet! It's approximately 500 feet from the main YC offices and set to debut in a few weeks at $100/month membership -- how could anyone not turn it down?
I'm the guy Sam was referring to who was looking for a place.
One thing that's bugged me about a few of the coworking spaces here is the idea of "hot-desking." If I have to go stake out a new place to work every day and have to lug my monitor with me, I might as well go work at a Starbucks.
I don't want a private office or anything, but if you're paying for a "full time" plan (as opposed to a lesser one), you should have some claim to a desk.
http://activspace.com/mission-2.html