I didn't think it would work, but when i plugged my Seagate FreeAgent Go hard drive, the unit recognized it and plays all mp3s and allows me to list and go to any folder... I have about 28 gigs of music on it...
Here some info: 250GB Seagate Free Agent Go P/N: 9ZA2A4-500
Update: so even with the hard drive, this thing is limited to roughly 2500 files...
it will parse all directories/folders until it reaches the folder and file limit, and will not display the rest of the folders.