There was a pretty good Dilbert on the weekend (not certain if it was new or syndicated) dealing with calling in to get tech support.
The scenario has some guy having problems with his device (which, in the picture, kind of resembles a PSU or optical drive). Dogbert, handling the tech support call, informs the guy that in order to get warranty support he needs to provide the device's serial no. first. Dogbert then informs the guy that the serial no. is conviniently located on a label placed inside the device. The guy looks at his device and then responds that there is a warning sticker on the case that states that opening the device voids his warranty. To this, Dogbert says something like "well, call me back if anything changes"