I'll admit, I'm kind of with Fishy on this.
Better graphics engines, but frankly I'm not sure that the machines are all that much of an upgrade.
Probably easier to code for, but then that is hardly a consumer's concern.
Heck, now that they are cheap, I might just buy an XBOX360 to hack around with and experiment with homebrew software.
I'd consider that with a PS3, but Sony really skimped on the XDR memory in that console.
Its a pity no one has documentation for the XBOX CPU, there are a ton of them available now, but they are useless except as repair parts.