I thought that Apple was going to do a big product release of *some* kind on April 1st, their 30th anniversary as a company. But, obviously, releasing Boot Camp, software that lets you easily install Windows XP on your Intel-based Mac, would really have been regarded as a practical joke, so they waited until today.
Dual-booting is really not that interesting. You don't really share files, and you can't switch back and forth without restarting the system and rebooting completely. I've been speculating if Apple will actually support Xen, an open source virtualization technology that lets you run multiple environments simultaneously. Perhaps Boot Camp is just a start -- Apple has already said that it will be included as part of Mac OS X 10.5, aka Leopard, so perhaps that is when Xen support will be rolled into the base of the operating system.
I'll be looking for mentions of Xen as people dig into the details of Boot Camp over the next couple of days.