I have a Philips DVD drive with a usb port, and was using a 1GB flash drive to play back video files copied from my PC. The drive failed relatively quickly - I'd had it for about a year, but hadn't used it all that often. I started to notice the video files were corrupt on playback, but initially suspected the file itself, or possibly a problem with the DVD player's decoder. I diagnosed the problem by copying a file onto the drive, then repeatedly checksumming it. The first couple of times, the checksum value would be often be correct, then on subsequent checks it would change on me. I'd end up seeing several different checksum values, never seeing it return to a previous value. Whether this was due to a problem in the interface harware when reading, or memory cells failing to retain their state, I don't know.
Even though it was a year old and I had no receipt, the manufacturer (Kingmax, I think?) was happy to send a free replacement. The new drive has seen much more use, but is still working fine.