Will upgrading to Mountain Lion allow USB Boot? One problem I have with my 2009 MBP running 10.6.8 Snow Leopard is that I can't boot from USB (well, I can, but only OS X in certain formats). I would really like to be able to boot linux from USB at will. I have heard this is possible on newer macs. Would this be possible for me if I were to update?
I have a MacBook from 2007 and it's possible to boot from USB without a problem.

Simply hold down - Option Key / (Alt) on Windows Keyboard on Boot and select where to boot from.

http://support.apple.com/kb/HT1310

If it doesn't work you might have to do a EFI Update

http://support.apple.com/kb/HT3260