Microsoft blogger (and all around nice guy)
Major Nelson has posted a series of articles comparing the potential performance of the Xbox 360 to the Playstation 3. It's a four part series which you can find
here,
here,
here, and
here. If that wasn't enough information for you, he's also got a podcast up
here with the engineers behind the posts. It gets a little technical but you're bound to learn something about the inner workings of the next generation of gaming machines.