I don't know exact numbers but I would say 35+ as some people come and go during the time but majority set up and stay the entire time. The last few years was in a hotel conference room and it started getting tight with the tables and gear set up to walk around.
You can look up the past events for the comments and see some pictures to get a feel.
For right now I do not have the time to organize something - my schedule is going to be pretty intense over the next year. However, if somebody else is up for it, I would definitely come. Otherwise, I may just go to the Chicago one in the summer.