Actually looking foward to USB 3, not the speed but the fact there is command queuing for usb storage, which makes ssd performant (without queuing you get far fewer iops, factor of about 10 from memory)
If you benchmark an SSD with and without queueing you get very different speeds; with hard drives there is still a difference, although not as much.
EDIT benchmarks (Intel SSD)
no queuing, 4k reads: 3965 iops depth 4 , 4k reads: 16,900 iops depth 8, 4k reads: 25,700 iops depth 16, 4k reads: 32,600 iops depth 32, 4k reads: 38,800 iops
The benefit decreases with larger reads, but still exists.