If you haven't gone, and don't mind the stag party atmosphere, this is an event that's definitely worth it if for nothing else then seeing all the M3s (and other Bimmers) in the garage together. It's just wow!
If you're into tracking, and they have a track day at LVMS, I can say the track itself is pretty fun. Flat, but long, with some very challenging corners. However, I wouldn't recommend it for any first-time trackers. The event (at least in 2011) was pretty loosely run, with no in-car instruction available, so it's definitely not ideal.
I'm not sure I will go, but if I do, I'll be skipping the track and going to the cars & coffee on Saturday morning instead.