Have you gone into your control panel and see if the drivers have a ! on them? if so, you have a driver problem.
I would boot into safe mode, go to device mgr and see what drivers (multi copies?) are installed and remove them.
Then boot back into normal mode and install the newest version of the drivers BEFORE plugging the usb cable in
It then should find the usb unit.
Another thing you can do since you are a single pc and mac guy, is grab the mac version of the drivers from their web site, and see if your mac see the unit.
If your mac dont see it, then it looks like a bad or damaged usb unit on the board....
Myk
RJ - something that might be added to the wiki on the build manual - have them test the usb module BEFORE its soldered to the board, then if it is bad, they can return it to mouser or where ever for replacement since it has not been soldered on.... just a thought....