"Why do birds suddenly appear/ whenever/ you are near?" I'm in love, ladies, gentlemen, and slashdotters. In love with the nicest little keystroke loggers you ever did see, the keyghosts (www.keyghost.com). These little bundles of Big Brother joy look just like some sort of PS/2 adaptor or extension cable, and can store 500kb of EVERYTHING that is typed on the keyboard.
You could swap these babies onto a person's box in 10 seconds, tops, and a nontechnical user would never notice. I'll be getting one of these soon - I wonder if I can use it to get teacher passwords at my high school? Shouldn't be too hard - just wander into the room when a teacher isn't there, plug in a keyghost, and walk away. Pointless fun, that.
Advice for anyone using this, though: if possible, you should use the keyghost with some sort of logging software as well. That gives you redundancy, and if someone gets suspicious they will tend to look for a software-based logger, find it, and go away happy. Just a thought.