I am new, and have been wondering if this can be done.
Yes.
Gerald
You can even boot from media on the USB host.
http://www.embeddedhobbyist.com/debian-tips/beaglebone-black/beaglebone-black-usb-boot/
William, did you notice any performance benefits from using the usb hdd?
Compared to netbooting, I lost around 1M/s reads, but doubled my write times.
So, 10.6MB/s reads, but ~20MB/s writes. I would not expect those speeds from a flash drive though, unless you have a super duper high performance model.