As f0dder said, you must distinguish between autorun and autoplay.
Autorun consists of reading a .ini file in the drive, and running the executable specified in that file. This is what makes viruses spread.
Autoplay consists of, when a drive is inserted, a dialog comes up with options like "read images", "read sounds", depending on the contents of the drive.
Now, the question here is that usb drives don't have Autorun, only cdroms. Thus, if you close the autoplay dialog, or select anything other than "run program" (which occasionally comes up in that dialog), or disable that dialog, there's no trouble.