Ah, the halcyon days of OS X, they seem to be coming to a close. What the hell am I talking about? Why, Apple's decision to close the kernel of OS X on their new Intel machines. This means that no longer can you recompile, slim down, or otherwise monkey around the kernel of OS X (if you are on Intel hardware).
Why would Apple suddenly turn very proprietary when they were yelling Open Source from the rooftops not so long ago (and you can still hack your kernel on pre-Intel hardware)? One word: piracy. Apple doesn't want some enterprising young hooligan to get OS X running on other Intel hardware.
Let's hope that Apple has a change of heart, since they themselves say that Darwin (the open source project that covers OS X's kernel) is in 'flux.'