Feel free to bring 360s for casuals! We need to stick to 1 system for consistency sake and so everyone can plan accordingly. The accepted Evo standard is PS3 so that's what we're rolling with. During the tournament we may need to throw a PS3 on your monitor to make things run quicker but outside the tournament fire that 360 up!
Also as a general note, all monitors should be played on by a few people to gauge the input lag. It's impossible for an LCD to be lag free, however it is possible for the input lag to be under 1 frame (16.7ms) which is more then acceptable in any game. And in games that don't have 1 frame tactics (like street fighter or virtua fighter) anything under 3 frames is acceptable as it's difficult for humans to perceive it. Once you start getting beyond 3 it will start messing with people who aren't used to it.