Re: Booting Ubuntu off external hard drive
I am not familiar with Macbook, but I do have several WD Passports that work fine for booting Ubuntu on PC's. You just need to make sure that you put grub on the USB drive and do whatever you need to do with the Macboot to boot from that when you want to. For some computers even if you change drive order to boot USB before internal, you may still have to press a specific key during BIOS splash screen to boot USB.
For Maverick the selection during install where to put grub is at the bottom of the manual partitioning screen, and you probably need to use that screen anyway to put Ubuntu on the external drive.
While USB 2.0 is not that fast, the WD Passport is as fast as the 4200 RPM drive in my old laptop, and faster than all but the best expensive USB sticks (which are not any faster).
i5 650 3.2 GHz, 8 GB, nvidia GTX 750 Ti, 32" 1080p | i7-4700MQ, 8 GB, Intel HD 4600/nvidia GTX 765M, 15.6" 1080p | etc.