Dan emailed me with an answer to a Firewire/USB question. These numbers are a bit hard to find, so for reference:
... USB is, as mentioned above, 500mA at 5V; FireWire can theoretically deliver up to 40V at 1.5 amps, though I don't know whether any FireWire adapter that can actually do that has ever been made. PC FireWire adapters run from the regular PSU 12V rail, and so can't deliver more than 12V at (mumble) amps, but even that's beyond the capabilities of USB.I love Dan's site -- I learn more there in a few minutes than any other site I visit.
It's easy enough to make an iPod charger that runs from a plugpack, car cigarette lighter or what have you, though; these go to a FireWire plug with only the power and ground terminals connected. You don't have to hack one up yourself, either; many exist in the commercial market:
Some are more practical than others, though: