I didn’t see it in the documentation or list of supported USB devices, but I have a D-Link DUB-H4 USB Hub working with the WD TV Mini.
It shows up as 4 different drives (one for each of the ports with something plugged into them). I’ve tried the hub both with and without power and it’s working fine either way. With power to the hub, the lights stay on when the WD TV Mini is turned off, but without power everything turns off when the WD TV Mini is turned off 
although not on the ‘official list’ of supported devices…this should work with almost ANY usb hub…
in fact, i would recommend this…as a usb stick plugged directly into your live box can get hot–and that could lead to drive failure…$5 for a cheap hub could save a $30 16gb drive…
also i have found many usb card readers work also—so if u have files on an sd/xd/cf card…they to can be read as if they are a usb stick…
good luck
-Peon
I guess I just didn’t expect the support for a hub would be there, but it’s a welcome surprise. I’ll second your advice on using a hub so your USB sticks don’t run so hot. Additionally, with a hub you’ll do a lot less swapping devices and thus less wear on the WD’s USB port.
I’m looking next to try a SATA>USB docking station with card reader. I’ll post again when I get it and try it out.