Re: Mac OS X 10.6 & Ubuntu 11.04
You may want to read my Web page on booting Ubuntu in EFI mode. Although it describes setting it up with rEFIt, the way it's set up is different enough that it may work better for you. Furthermore, if you prefer, you can configure GRUB to be the computer's primary boot selector. This will require some deviations, and possibly a custom GRUB entry to get it to launch Apple's .efi boot file, but it should work, at least in principle.
If I've suggested a solution to a problem and you're not the original poster, do not try my solution! Problems can seem similar but be different, and a good solution to one problem can make another worse. Post a new thread with your problem details.