Apple has hidden a poem inside OS X that warns users not to pirate the operating system.

There once was was a user that whined
his existing OS was so blind,
he'd do better to pirate
an OS that ran great
but found his hardware declined.
Please don't steal Mac OS!
Really, that's way uncool.

What's the deal?

Basically, Apple wants to make it hard to run its Intel-based OS X on PCs, by AES-encrypting some key applications like Finder, Dock, and Rosetta (ha, sounds like instruction-set randomization again!). Of course, there must be something behind the scene to restore (read: decrypt) the scrambled binaries. Apple uses a kernel extension dsmos (/System/Library/Extensions/Dont Steal Mac OS X.kext) to do this job. For now this decryption is all done in software, and I suppose the binaries are statically encrypted with fixed keys. So this extra protection doesn't help much with defeating piracy. In the future though, I'd expect Apple to make use of TPM to authenticate the hardware and do the decryption.

The major obstacle of OS X86 (aka Hackintosh), is that legacy PCs only come with BIOS, but OS X only runs on EFI. Hackers had to either patch the kernel to remove its dependence on EFI, or patch the bootloader to emulate EFI so that the vanilla kernel can run. Ironically, Apple had the same problem the other way around: it upgraded its EFI to include BIOS support so that Windows XP can run. Besides the EFI hack, SSE3 instructions in the kernel have to be patched or emulated on old CPUs.