Nothing to worry about at all. This is normal behaviour under Unix. If you check the contents of the folders you will probably find that they are either empty or report as 0 bytes. I'm not sure what conditions have to be met for those files to appear, they show up from time to time in my basket as well.
I do know that I can cause those files to appear by doing a forced shut-down (holding down the power button until the unit shuts down). In those cases the Recovered Files are likely the result of the Journalling file system cleaning itself up after a forced shut-down.
This is fine. You'll find that if you're having an iChat conversation and friends send you pictures or mp3s, when you restart, they will typically be in the trash, which is nice, because if you forget to save something, you can pull it out.