By now, many reports point to actual, verifiable instances of “hacked” Mac OS X running on more-or-less standard PCs. I wrote a few days ago:
Rainer Brockerhoff wrote:

…However, from what I’ve read on the net, the Mac OS X boot process checks for the presence of the TPM chip and later on uses it to verify, or decrypt, some parts of its own object code

It therefore appears that – at least in the current, very preliminary version used – they’re simply verifying, not decrypting.

What I find somewhat funny about the situation is that certainly Apple is following these exploits very carefully and is, in effect, using these people to define and refine the protection technology that will be used in the final product. These are truly interesting times.