I'm a recent Mac & Parallels convert, and I spent a long time trying to set up my machine (a MacBook Pro) to native-boot MacOS, Windows, and Linux, and to be able to boot the same Windows and Linux partitions as guests in Parallels.
I only had partial success, but perhaps some of the info will be useful to you.
I have a bunch of GUID partitions (two for each OS: system and user) plus an extra dummy MacOS install, plus the Lion Recovery partitions that get automagically created when you install Lion into a partition. My hybrid MBR lists the Windows and Linux partitions, but I can only native-boot Dummy MacOSX, Main Mac OSX and Windows (never could figure out how to native-boot Linux).
Parallels can also boot the Windows partition.
To get Parallels to boot the Linux partitions, the best solution I could find was to create a small virtual disk and mount it as /boot when installing linux. Most of the Linux system goes on real GUID partitions, but Grub and the kernel stuff goes on /boot. Then, in the Parallels VM setup, I have the virtual disk mounted as Hard Disk 1, and the other partitions connected as Hard Disk 2.
Some day I'll figure out GPT booting and put the Linux /boot in one of the extra Mac OSX recovery partitions (650MB), then be able to boot natively from the reboot-option-key menu. But today is not that day.
Good luck!