Running Wheezy on a RPi B, with a 2 amp power supply, 2x 32 Gig. USB SANDISK memory sticks.
The first memory stick ( /dev/sda1 ) is mounted using UUID, system boots quickly. Add second identical memory stick, ( /dev/sdb1 ), mounted this stick using /dev/sdb1 in fstab and have very little difference in boot time. Changing /dev/sdb1 to the UUID of this device easily adds 40 seconds to the boot time. This is not critical, but I am curious, why the difference?