Like the one I just had. See, for this server I've set up, I have a vast multitude of hard drives plugged into it (currently 8, with space for 3 more (leaving the 12th ide slot for a CD drive for disaster recovery purposes)). Seeing as how they are identical, and literally lined up on a piece of cardboard outside the computer case, trying to find a specific one to replace was promising to be a daunting task -- one which I had yet to think of an easy way around.
Well, as I mentioned, I have a few test files that I'm using to do filesystem tests (only way to check a drive is to actually *use* the bloody thing), and I just kinda glanced over there after starting one such test and noticed that I can see the little light on the drive registering activity. "Hey," thinks I, "I could just label the damn thing while it's light is on!"
Why I didn't think of this before, I'll never know.
So, now next to the server's case, I still have a row of identical hard drives, but taped to one is a nice piece of paper declaring it "/dev/hde". I'll be filling out the rest as I bring them into service.