Before everyone starts complaining about the palpable layer of polyurethane coating every surface in the demo, consider Carmack's claim that if he had four more days, the demo would be twice as smooth. That's just it, Mr. Carmack, it's already too smooth. But we know it's early so we'll just study this video until we get to see more (like your special Mac-related announcement) at E3.
If you'd rather avoid the embedded YouTube shakycam footage, you can watch Apple's much nicer streaming version of the 2007 WWDC keynote (jump ahead to 11:30).

