You know, I was having that problem on my motherboard as well. I had a new external disk drive and the USB only worked at standard speed. I gave up and switched it to firewire.

Funny thing is, I remember USB 2.0 working when I plugged in the Karma during the beta testing phase. So I dunno what changed. Or perhaps nothing changed, and it was the device itself that was giving me grief.

Check your BIOS settings, mine had settings related to that. And the funny thing is, the names of the settings were counter-intuitive, so you weren't sure which was the fastest setting until after you looked at the help text.

Edit: I was also using an Asus motherboard, a P4C800 Deluxe. Wonder if that's a factor?