Others have commented on how the style of the iTunes 5.0 interface is different than any other Mac OS X 10.4 “Tiger” application. What’s more interesting to me is the contents of the new interface.
They finally added groups! I mean, folders. But they kept most of the wacky, colorful smart groups, I mean, sources, from 4.9:
All of this leads me to rule #1 (No, not that rule #1!):
Any sufficiently advanced Mac OS X application is indistinguishable from Xcode.