I know it's possible, but in the machines I've had to do it on, it's definitely non-standard. USB booting is pretty common in most modern bios's, however don't

I know it's possible, but in the machines I've had to do it on, it's definitely non-standard. USB booting is pretty common in most modern bios's, however don't forget we're talking about Apple here, where they control the entire stack. Booting off external drive on Mac (power on + option key) has been in place for many generations of their hardware. It's definitely patchy in Windows land, esp with net books.