Booting from USB to install Windows 7 on Macbook Pro, Early 2011 I used Bootcamp (5.0) to create a Windows 7 install USB. It successfully created the install USB but when I reboot the system and hold down the option-key to boot from the USB drive, the boot-loader doesn't give me the option of booting from USB. 

I also tried recreating the install USB from another Windows 7 machine using Microsoft's own Windows 7 USB creation tool but I still don't get the option of booting from USB on my mac.
What am I doing wrong here? Any Ideas?
You need to format the USB drive to use the GUID partition type -- use the Disk Utility on your Mac.

source Apple support docs