If you have a MS Windows computer, to remove U3 from your flash drives and make them usable with your slug you can use Geeksquad's U3_Uninstall application.
This can be downloaded from U3's site here: http://u3.com
At this time there is no known remover tools for any operating system rather than Windows.
WARNING: Running the program at the sites listed above will remove U3 from your flash drive permanently. It will also reformat your drive, so make sure to backup anything you wish to keep.