[The Godfather]

I am on the brink or compromising maintained rate for burst rate, for the sake of my wallet. I decided that I don't mind slower backups, if iMovie renders don't slowdown. However, with the scrubbing feature of iMovie '08, the question comes up again: will USB HDDs choke where Firewire HDDs shine?

[slpdLoad]

Firewire is faster, hands down. I can't speak to whether USB would be enough for iMovie, but I've never had any problems with Firewire (400 or 800), and I've had bandwidth issues while using USB 2.0 drives along with other USB devices. Shop around, I'd bet you can get a Firewire enclosure to put a HD in for not too much more than a USB enclosure. YMMV.

[mduell]

Many enclosures have FW and USB for the same price as a FW enclosure, so you could get one with both and try them. I'd like to hear the results, if both are adequate and/or if one is better than the other.
A lot of USB chipsets (either on the computer side or the enclosure side) don't seem to support isochronous transfers very well, which may hurt performance for something like this.