I would also be interested in this capability, not really as extra storage (would be awkward for me to have a USB drive hanging off my phone all the time) but to exchange files. I know there are many other ways to pass around a file, but sometimes USB drives are used to pass around files and it would be convenient to be able to take it onto my phone without having to go through a computer.
Also, I wonder if this might be more possible on my HTC Hero since that already plays "host" to the removable micro-sd card...
Regards,
Hudson