I just found another page with more info on this:
http://www.kenwood.com/usb/english.htmlThis lists the compatible USB devices as well as the specs and limitations of the Kenwood interface.
Any device belonging to the "USB Mass Storage" class is supported. This would include pretty much any USB hard drive, memory card, etc. as well as many hard drive players, including iPod.
The maximum number of files supported through the Kenwood interface is 15,000, in maximum 500 folders. This is the main difference between the USB interface and the Phatbox -- Phatbox supports 30,000 files (at least theoretically). Still, 15,000 songs should suit the vast majority of people.
Better information on USB interface models can be found on the European Kenwood websites. I think I'm going to wait until Kenwood ships a USB model with one of their higher-end (OEL) displays -- because those will display album art!
Still, looking forward to a hands-on report!