Question: I've read everywhere that you can't have more than 4 partitions because of GPT on intel Macs. But what happens if you make more than 4? On my iMac I have EFI, Macintosh HD, Windows, Linux, and Linux swap partitions and I am able to boot from all three operating systems with rEFIt. So, I have 5 partitions, so why does it work? I made the partitions with Snow Leopard's Disk Utility by the way.

Answer: 
While Windows 7 x86\_64 supports GPT, it only supports UEFI or BIOS. Windows 7 does not support "Apple EFI" which is an amalgam of Intel EFI 1.1, and some bits of Apple's own and some bits of UEFI 2.x. It is not strictly a UEFI 2.x implementation which is what all non-Mac OS operating systems require. So this in effect limits Bootcamp (or rEFIt) users to using the CSM (BIOS), and thus require an MBR since BIOS only understands MBRs.

MBR=4 partitions, but 1 of which is reserved when it's a hybrid MBR, as mentioned it's to indicate that the entire drive is GPT so that you have some warning from an MBR-only aware partitioning application. So in effect hybrid MBR is limited to 3 partitions.

In theory you can choose which 3 of the potentially 128 GPT partitions you want exported to the hybrid MBR. But most tools don't let you do this. The only one I know that does is gdisk.

I agree that hybrid MBR is standards-violating and is a bastardization. My preference would be for Apple to issue a fully standards compliant UEFI 2.x firmware for all machines sold in the past few years. In particular it's annoying as balls that brand new machines sold today still are based on Intel EFI 1.1, not UEFI 2.x.
The problem here is that, as cmurphy says, Windows (x64) can't use Apple's EFI implementation(which is basically EFI 1.1). It needs either UEFI (EFI 2.0) or BIOS. But because Windows has an [artificial limitation](http://www.rodsbooks.com/gdisk/booting.html) of tying up UEFI to GPT disks and BIOS to MBR disks, it needs some trickery to work. Specifically, Windows and OS X on an EFI 1.1 can coexist on a single drive "only" if Windows is fooled into thinking it's an MBR drive while it's actually GPT (OS X does not support MBR). This trickery is what is called Hybrid MBR - it's a dangerous and ugly hack like cmurphy says. 

However, you CAN boot windows on GPT from BIOS *IF* you have any *small* MBR drive you can boot off, or even a floppy. It's not even a hack and will even work on Windows 32-bit.

Basically Boot into the Windows install/repair disc. Just create the system drive on the floppy, and use `bcdboot` to put your boot files on the floppy. Add a bootsector with `bootsect`. Change the `{bootmgr}` `device` to `boot`. Boot from floppy.

Steps are detailed [here](http://www.sevenforums.com/installation-setup/320700-boot-windows-7-8-gpt-bios-system-no-hybrid-mbrs-duet.html).