Not much has changed stylistically, but they can drive the 30-inch apple display now. Apparently the keyboard backlighting is 10 times brighter, you can scroll using the trackpad (that seems like something you should be able to do with software on an older machine too), and they can automatically park the heads on your hard drive if you drop the machine.
I wish I were rich so I could afford to buy a new machine every time apple comes up with something new and cool.
I think I'll have to wait for the G5 powerbook. It shouldn't be too many more months.