I don't know much about it, but you should check out the six flags site -
www.sixflags.com - (Well the site got changed, but that brings you to it anyway

). I think it's on a first come, first serve basis, so you should try to get there early if you want to use it. I never used it since I only go from 7-10 or 5-8 or something, so the tickets are already gone.