I have an old 3G Firewire iPod and a several USB iPods. The old Firewire iPod is a joy to sync. Extremely fast, instant dismount. The modern USB devices are a pain. My Mac Firewire connected drive feels as fast as an internal drive, my PC USB drives are sluggish.
Gigabit ethernet connected drives, in my experience with my CPUs in heavy use, are much faster than local USB drives and even comparable to local Firewire 400 connections.
This, of course, contradicts the theoretical performance figures for USB drives. It makes me mourn the lost beauty of Firewire 400.
So I really enjoyed this discussion of Firewire, USB and SATA on Macs, with Windows specific footnotes.
USB has a faster theoretical maximum than Firewire 400 (400 Mbits/sec; 50 MB/sec), but Firewire 400 is actually much faster than USB because it uses smarter peer to peer interface hardware rather than pushing low level work onto the PC host's CPU as the simpler master to slave architecture of USB does.
On a Mac, Firewire is typically around twice as fast in real world transfer rates, with USB hitting around 18 MB/sec and Firewire reaching 35 MB/sec throughput. Windows' implementation of USB has historically been faster than Mac OS X's, with Windows' USB reaching throughput closer to 33MB/sec..
Firewire on a Mac is far faster than USB on an XP box, I suspect Firewire on XP is comparable to Firewire in OS X and also much faster than USB in real world use (ie. when the CPU is loaded down with other tasks, and so unable to respond to USB demands).
Given my experience I'd expect a USB drive on an gigabit wired Airport base station to be significantly slower than a SATA drive inside a wired Time Machine. I hope that will be tested in a future post.