I'll be buying it -- just not day one. I've got too many games to finish and I wont be ready when it comes out.
One question, though, for the people who always ask if Halo 3 will move systems: Halo 1 and 2 were both original Xbox. Yes, they are backward compatible on the Xbox 360, but Halo 3 is the first of the series that has been developed on the 360 and will therefore have significantly better graphics and such. How the heck could it NOT sell consoles?