My 12.10 computer has several accounts on it. My wife has a Kindle Keyboard 3G that she manages with Calibre. The problem is that every time she tries to eject the device in Calibre if asks for my password. Mine is the main administrative account which may be why it wants my password.
I'm not at the computer so am not positive whether I could eject from the file manager without a password, though I know that other USB flash drives don't require it.