Actually, this is pretty much what Mactel uses. They implement a GPT-MBR hybrid, which has frustrated me greatly every time I have tried to work with it. There were two big problems:
1) Because you are mirroring everything on the MBR, you can't have more than 4 bootable partitions. This sounds like plenty, but the bootable ones have to be the first four on the GPT, and Apple--don't ask me why--decided they need the first three (at least on my computer). So you can only dual boot, which is frustrating for those who want Linux, Mac, and Windows (like me). 2) A more specific problem: When I was booting Debian, on install I would have to sync the GPT with the MBR after partitioning so things were lined up, and then install GRUB to the MBR. Didn't realize why I was supposed to do this until I'd made Debian unbootable for the fourth time. Basically, the GPT was getting synced with the MBR after GRUB had been written to the MBR, which overwrote GRUB, and stopped me from booting Linux. This meant that if I wanted to keep Debian (and I'm assuming it would be the same with any Linux distro using GRUB as a boot loader) I had to avoid partitioning again, and avoid Mac updates as the next one included an EFI update (which I eventually installed and, of course, made Debian unbootable with).
no subject
1) Because you are mirroring everything on the MBR, you can't have more than 4 bootable partitions. This sounds like plenty, but the bootable ones have to be the first four on the GPT, and Apple--don't ask me why--decided they need the first three (at least on my computer). So you can only dual boot, which is frustrating for those who want Linux, Mac, and Windows (like me).
2) A more specific problem: When I was booting Debian, on install I would have to sync the GPT with the MBR after partitioning so things were lined up, and then install GRUB to the MBR. Didn't realize why I was supposed to do this until I'd made Debian unbootable for the fourth time. Basically, the GPT was getting synced with the MBR after GRUB had been written to the MBR, which overwrote GRUB, and stopped me from booting Linux. This meant that if I wanted to keep Debian (and I'm assuming it would be the same with any Linux distro using GRUB as a boot loader) I had to avoid partitioning again, and avoid Mac updates as the next one included an EFI update (which I eventually installed and, of course, made Debian unbootable with).
So yeah. Doesn't work that well.