I've had problems with file corruption on thumb drives with little hard disks inside (Kaser Jumbo 4GB). I've had two external hard disks dying, one of them almost new. I've also broken a flash drive, but that was my fault because I dropped it on the street. My current strategy is to copy the important things to a second internal hard disk at the end of the day, and also on the flash drive. Whenever I reach 4 GB I write a DVD+R. The only thing that can really mess this up is a smart virus, I guess, but not hardware failures. Even the virus can only damage the current files, not what's already on DVD+R, of course.