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: 
Intel-based Macs use the GUID Partition Table (GPT) by default. GPT in turn supports up to 128 partitions by default (that value can be increased if necessary, although most partition tools don't enable you to do so). Thus, there's no problem with having more than four partitions on an Intel-based Mac.

The limitation you've heard about is a distortion of the limitation on hybrid MBRs, which are a dangerous and standards-violating hybridization of GPT with the older Master Boot Record (MBR) partitioning system used on most PCs. In a hybrid MBR, up to *three* of the GPT's partitions are duplicated in an MBR data structure. MBR is limited to four *primary* partitions, and in a hybrid MBR the fourth primary partition is occupied by a special partition that identifies the disk as being a GPT disk. This fourth partition is often mistaken for an MBR-side duplicate of the EFI System Partition (ESP) that's present on most GPT disks, but it's not that.

Apple uses hybrid MBRs to enable Windows to dual-boot with OS X on Macs. Windows favors the MBR data structures, so it sees the disk as being an MBR disk, whereas OS X favors GPT data structures, so it sees the disk as being a GPT disk. (Linux, like OS X, sees a hybrid MBR as a GPT disk.) A hybrid MBR doesn't limit the number of GPT partitions you may have, but it does limit the number of partitions that the Windows installation can see, to no more than three.

Note that extended partitions and Extended Boot Records (EBRs) have nothing to do with hybrid MBRs -- or at least, they shouldn't! In the MBR scheme, extended partitions serve as placeholders for logical partitions, which are defined by EBRs. Using this scheme, an MBR disk can support a huge number of partitions -- theoretically about half as many as there are sectors on the disk, although practical limits are much lower than that. Disks with hybrid MBRs don't use extended partitions, though, because maintaining consistency between the GPT and MBR sides of the disk -- already a challenging enough task with regular hybrid MBRs -- would become much tougher.
I found [this article](http://www.rickycampbell.com/the-intel-mac-partitioning-system-efi-and-gpt/) which explains the partitioning scheme.

Essentially, if I understand the article correctly, there is an “Extended Boot Record” on one of the partitions on one of the primary four partitions which describes the extra "extended" partitions. Some legacy operating systems cannot see them.

Linux can see the extended partitions after the kernel is loaded. I presume you're able to boot properly because the Linux partition is on one of the four "primary" partitions.