Another strange thing is that I can't access the Apple Hardware Test via either of the usual ways (power on while holding D or F2). I also can't access my OS X DVD either because my USB port isn't working (i.e. I can't access the CD/DVD drive).
Anyone got any tips on how to proceed? Unfortunately, I suspect a call to Apple may be in order...
EDIT: I've tried resetting the NVRAM (option+cmd+r+p), as well as doing another clean reinstall of OS X using remote disk. Neither have done anything. Safe mode doesn't make it better either.
Any other suggestions would be more than welcome...
EDIT #2: Just in case anyone is following this in the future, it turned out to be that the USB/hatch cables needed to be reseated. Completely un-software-related, despite the fact that it appeared to stem from my system update and attempted Boot Camp installation.