GRUB2 installs an EFI bootable file into the EFI partiton, the same way OS X does. GRUB is capable of booting Linux, Windows an OS X in EFI mode very similarly to how it works on BIOS-based setups.
The consequence of running Linux on EFI instead of on BIOS is that certain things which depend on a BIOS being present (like the proprietary nVidia drivers, for instance) won't function. I don't have any experience with ATI hardware, but I can say that the open-source nouveau driver works quite nicely in EFI mode.
From personal experience I can say that, although it can be somewhat difficult to setup, Linux on EFI is quite stable. I've been using Linux almost exclusively on my MacBook Pro for the last 6 months or so without any trouble. Additionally, I can cite the fact that popular Linux distributions (like Ubuntu, for instance) consider this setup quite stable - their stable LiveCDs have implemented this setup for quite a while now.