After turning on my desktop one day, I found that my CPU usage was maxed out at 100%, with most of that going to hardware "Interrupts":
I tried to enable/disable all my devices one by one through the device manager, and found that I could get the CPU usage used by the Interrupts down to 50% by disabling all devices labelled "USB Host Controller" (except the ones for the mouse/keyboard). I found that I also got 10-20% more from disabling "High Definition Audio Controller".
Following the tutorial at: http://www.msfn.org/board/topic/140263-how-to-get-the-cause-of-high-cpu-usage-by-dpc-interrupt/
Led me to similar conclusions (that is, that the culprit is mostly "USB Host Controller"):
I've tried updating my asus motherboard driver and my video card driver. This is on Windows 7 64 bit.
I've spent hours trying to figure this out and I'm running out of ideas short of formatting (which might still not fix it!).