If you're gaming at 1920x1200 or below and not interested in overclocking then the GTX570 is definitely the way to go.
The 480 comes into it's own at 2560x1600/1440 and higher levels of IQ (8xMSAA, advanced tesselation, ambient occlusion etc.) due to a wider memory bus and frame buffer more than offsetting the lower clocks. The 480 is in general a better overclocker, but at the expense (both in stock and OC'ed form)- as Mizzou pointed out- of greater power usage and attendant heat and noise output.