It would appear that the integrated EHCI controller on AMD's chipsets is a real pain. The previous issue I was having with it may have gone away with a kernel upgrade (or not - I'm not 100% sure) but now something new has reared its ugly head. I bought a Logitech UVC webcam recently, and if I'm actively using any other high-speed USB device, trying to use the webcam causes the entire EHCI controller hangs with a "force halt" error half the time. What's more, it looks like I'm not the only one having this problem - it happens across a wide range of different SB600-based systems with many different UVC webcams.

Edit: Bleh, could someone move this to the right section *facepalm*?