I've been seeing this trend pickup alot of momentum here Stateside. Its been quite popular in Japan for a couple years now.

Basic concept
Staggered width and offset... can run slightly wider rim in the front for maximum grip and keep sidewall flex to an absolute minimum for maximum stearing response. Keep the same size tires on both sets. Use wider front rims to minimize sidewall flex therefore improving turn-in.

I know theres alot of "Wheel heads" here that will love this topic. Let the fun begin! Oops..edit