i've done it through FireWire from my iPod, and it wasn't setting any new computing speed records, but it was useable. FireWire 800 should be pretty good.
TimJim; FireWire 400 is about the same speed as USB 2.0, or even faster for extended data transfers. FireWire 800 is much faster than USB 2.0.
USB is great for burst data transfers, such as documents from a memory stick, or a few songs to an iPod, but it chokes as soon as you transfer anything with some beef to it, such as video files, or OS information. It is also CPU reliant, meaning if you are already doing something else with the CPU (which is likely if you are running an OS), the speed will decrease even more.
FireWire, on the other hand, is a broadband connection; data can simultaneously come in and out of devices. It also has its own hardware controller, so you could be folding, and still get maximum speed out of it. FW400 has better sustained transfer rates than USB (about 10 MB/s faster), and thus is more appropriate for large data transfers, such as video from a camera, or digital audio from a studio mixer. This is one of the reasons Apple are claimed to be better for any kind of media or digital art; because for almost 10 years, Apple have had this in all their computers.