I didn't realize until just now that USB 2 flash drives are much slower than hard drives. It's roughly 25MB/sec vs 60/MB sec. Really surprises me, as it's solid state vs mechanical.
USB 2 has a theoretical throughput of about 480 megabits per second (roughly 40 megabytes ish/second).. there are a few usb pen drives which get close, even if you put a hard drive which can do 100 Megabytes/second on a ussb2 cable it'll be throttled down to the 4*MB mark... I believe in theory u can burst to 60MB/sec but not for long due to latency.