I don't think they wear out as such, although there may be a limit to how many read/writes they can perform before they start to get untrustworthy. Whatever: make sure you back up any important files on them?
That was quick
Yes I have been rewriting this stick a lot
I do have a robust back up system and considering the relative cheapness of memory sticks it may be prudent to put this one out to graze
Apart from the fact that technology leads us to ever growing capacities and speeds and therefore sometimes rendering certain mem card / stick sizes such as 16Mb or 32Mb obsolete, it is worthwile to note that memory cards /sticks have a limited life expectancy.
There is a difference; single layer cards /sticks may allow in excess of maybe 100,000 read-write actions, whilst multi-layer cards may only allow around 10,000 to 15,000.