Single boot Linux without delay
1. If you have OSX installed, boot to it and mute sound. This assures that you won't be annoyed by the startup/poweron sound afterwards. I even used This software to be absolutely sure.
Restart to confirm that no startup sound is audible.
2. Prepare rEFIt boot disk (CD-RW).
3. Boot Ubuntu install and remove all partitions, partition as you like for your Linux installation. Install Ubuntu, restart.
4. Put in rEFIt CD and holding down alt key, boot rEFIT cd. Synchronize GUID and MBR. Restart.
5. Insert OSX disc, boot from it, open terminal and enter following:
bless --device /dev/disk0s2 --setBoot --legacy --verbose
where /dev/disk0s2 is the partition you installed grub (do 'diskutil list' to find out correct partition). Of course, '--verbose' is optional. This makes Macbook EFI firmware boot your Linux installation in legacy mode without long delay (20s vs 3s).
6. Restart your Mac (don't forget to remove OSX disc). And boot directly to Linux!