So MBR is terrible, everyone who has ever had the pleasure of dealing with it with its quirks and massive rule book will likely attest.
So I rebuilt my system today, Windows 7 64 in UEFI/GPT "mode," then I installed the Windows 8 Dev' Preview side by side also in EFI/GPT mode.
What I was expecting was to be able to select which boot loader to run up from my BIOS, what I actually got was one completely inaccessible OS and no functional tools in either Windows 7 or Windows 8 to fix the problem.
Essentially what should happen is Microsoft should be making a new entry in the uEFI for each Operating System, or updating a single boot loader to support several OSs.
What Microsoft actually does is delete the Windows 7 bootloader, replace it with the Windows 8 bootloader, and ultimately leave your older operating systems stranded.
This all wouldn't be so bad if it happened to a MBR system because on a MBR system you have a handful of tools to fix this issue like BootRec, BCDEdit, DiskPart, etc.
Unfortunately all of these tools target the "fake" MBR, as does as the automatic tat' the Windows DVD ships with.
Also, while we're on the subject of the Windows DVD repair mode, is it just me or has anyone else noticed it gets worse and worse with every Windows version?
Depending on how how I boot into the Windows 7 DVD sometimes I am literally unable to start even the console because it brings up an error ("No compatible version of the OS is installed"). Luckily I know the secret key-combo (Shift-F10).
Also they replaced it with Metro-style tat on Windows 8, and the default option is "Continue to load Windows 8" which is all levels of stupid in the frigging repair menu. The automatic stuff is still there but now hidden under a dozen sub-menus, and the console is now Troubleshooting -> Advanced -> Repair -> Console or something. Nothing "useful" has been added.
I know what you will say - "It is a developer preview, please shut up!" and while that is a fair statement, everything I said could equally be aimed at Windows 7. Windows 7 lacks tools for UEFI, and Windows 7's bootloader is not REALLY designed for UEFI.
So my opinion: Stay the heck away from UEFI for a while. At least as far as your bootloaders/partition tables go. It might be a fine "BIOS" but that is as far as it goes.