I've wondered about the same thing.

Some thoughts:
-If the printer is USB, what is stopping someone from just printing out the file.
-If on a 2000/XP system and setup properly, the files user permissions should lock out anyone who should not have rights to view file.
-Good way to sneak in a file though.
-As far as I know, you cant boot from a USB device.
-If security is a concern, maybe use a dumb terminal.