I haven't been to noisebridge (yet), but from the people I've talked to at relatively large events like SuperHappyDevHouse, there's a quite a few smaller, informal groups of hackers getting together to work on stuff. It's just that most of these occur in peoples' apartments, so they're not open to the public. If you're interested in finding some place like this, though, I recommend you try and meet people somewhere like SHDH.