I have had very mixed results using flash drives for this type of application (not with dish receivers, but other setups). Being solid state is nice, but they do have a failure rate that increases significantly the more they get used and this type of setup seems to hammer the storage medium heavily.
A good idea of what happens is when I did an experiment with 4 USB flash drives setup as a RAID 5 config. Just for kicks, I copied gigs of data to the drive, removed a USB stick and reinserted to rebuild the array. Seemed ok for a while, but within a week or so, 2 of the sticks failed completely and reported no storage space.