I was going to make that point as well.  I posted a question on ComputerTalk a little while back, and DKO responded saying that USB drives are not the best for long-term storage - just the way they are designed. 

Mrs B, if you are looking for long-term safe-keeping, maybe buying and keeping a CD/ DVD device is just the better option.  I am not an expert on this, so maybe someone else can speak to this as well.