The GUID specification calls for a "protective MBR" with exactly ONE partition (with an ID of 0xEE). No matter how many partitions you create in the GUID table, there should only be ONE partition in the MBR table. ONE!
What Apple has done is make a hybrid GPT/MBR. In this case, "hybrid" is synonymous with "bastardized". Any partition you create (with apple tools) in the GUID table gets copied to the MBR table. This is why when you install bootcamp, you CANNOT remove the partition and recreate it; the geometry would not match what is in the GUID table. Once the two tables are out of sync, it's a real bastard to fix. ReFIT has a program called gptsync that will sync one way; GTP to MBR... but there is no reversal of that.
The really funny part is Apple's Tech Note from 2006 (probably just before BootCamp). They describe the Protective MBR as "a single partition entry (of type 0xEE) that covers the entire area of the disk used by GPT structures and partitions." A single parition? A Bootcamp Mac has three!
Furthermore, Apple mentions "Specifically, if block 0 contains an MBR with more than one partition entry, or a single partition entry whose
OSTypeis not 0xEE, it is not a compliant GPT disk, and manipulating the GPT may cause dangerous inconsistencies between it and the legacy MBR."
and they follow that with a:
WARNING: Failure to comply with this recommendation may result in the loss of user data.
So there you have it... Apple's GPT support is completely laughable and confusing as hell. They completely violate their own recommendations not to mention the specs.
Ironically, I can use Apple's DiskUtility to format a Leopard Mac with good old MBR and 2 partitions. I can restore a Windows XP image (via RapiDeploy) and a Mac image (via netinstall) to these partitions, and THEY ARE BOTH BOOTABLE just FINE. The caveat is, you can only boot from EFI (holding the option key). Once you're in Mac OS or Windows, NONE of your disks appear in the startup disk preference pane (you can't even select the disk you are booted to). It's kinda sad when EFI is smarter than your proper OS...
Don't get me wrong; EFI and GPT are totally awesome technologies-- I just hope we can stick to the standards. This means Microsoft: Get on the ball and support EFI and GPT for Windows XP and Vista. And to Apple: Why don't you stick with MBR for dual-boot Macs? You only support 2 usable partitions anyway!