I have to agree with sej on this one. I'm a huge advocate of firewire. My coworkers often make fun of me for it, especially now that firewire is all but dead. However, firewire is WAY faster than USB2 even though it's "only" 400mbps. USB2's *theoretical* output is 480mbps but that is max throughput and hardly sustainable. Now, when we get to USB3 then we can talk.
SATA is MUCH more consistent with their speed than USB is and will therefore give a real world advantage over USB in sustained data transfers. Nonetheless, back to the original topic, I maintain that the USB HD DVD drive gives enough performance to make it useful. You can certainly play movies back with no problems. As far as ripping goes, I don't have a comparison to draw from. Meaning that a SATA drive could very well be much faster than the USB drive....or it may not. I simply don't know.