For the other Mac users out there... you're usb drives need to formatted in MS-DOS (FAT) to work with the eDGe. If they are formatted to Mac OS, the device recognizes that there is a drive connected but can't read it. You get a greyed out icon with and exclamation mark in the left corner of the notification bar, but it can't recognize the disk.

I had forgotten that I had reformatted a couple of my usb drives... and was a little puzzled by this for a while.