The RS Components catalogue on CD...
At a client site doing some desktop support stuff and get a call from a bloke in the mechanical engineering office, saying his CD isn't reading properly.
So I wander up and he's sat there cursing the PC, that the CD drive is crap etc.
So i press eject and out comes the RS Components CD, which he tells me he's just gotten as people keep nicking his paper copy, but they won't be nicking that. It's at that point i see he's helpfully scratched his initials into the printed side of the CD, nice and deep so no mistaking it's his, and you can see clear through the disk!