IMO, you should wait a couple of months. Like all consoles when they first come out, the 360 is seeing some "bugs" and other problems right now. Somethign about some piece of foil that should of been removed on some of them that weren't removed and it's causing some over heating issues. Plus some other stuff. I always wait until they get all that stuff ironed out before I buy one.
I won't be buying one till September when Splinter Cell: Double Agent comes out. Maybe sooner if a game comes out that I really want to play. But as of right now, not till september.