I just wanted to point out something those of you attending WWDC will see.
Apple is going to change it's kernel or at least the layer that interacts with the hardware. It's going to be a version of Xen. Apple's move is because of it's plan to take advantage of virtualization built into the intel chipset. There is big changes coming to 10.5, and they are really, really good.
How Long Will Apple Keep the MACH Microkernel?