If you've purchased a new USB Thumb Drive recently you may have run into this problem: U3.
U3 is a functionality built into several new thumb drives (namely of the "SanDisk" family), that allows you to run applications right off the drive.

The thing is, that when you insert your thumb drive, U3 will actually mount itself as an additional drive. This can be quite frustrating. Especially if you don't even want to use the applications that come with U3; not to mention the disk space that is exhausted for the install.

Well you're in luck, if you want to destroy that pesky U3 launchpad, download the uninstaller here: http://www.u3.com/uninstall/, and zap the bug.
The removal utility will format your thumb drive, so make sure to back up all the data stored on it.