I have an aching shoulder. This is because I have been concentrating very hard on a particular task for a few solid hours this morning, which I suppose has made me tense up a bit, and my shoulder seems to have seized up as a result. It could also be because I'm not using my RSI-avoiding padded wrist rest. Sadly, that item has been put to other uses, namely as a brilliant fly-swat. As Rob pointed out at the weekend, it is ironic that a device designed to lower the likelihood of RSI is being actively misused on a task that employs a wrist-flicking motion, repeated over and over again. He suggested adding in a slight right-left movement (he used a fancier word which I've forgotten) which apparently would really guarantee that I'd give myself repetitive strain injury (think of the perpetual small movements made in using a mouse). I seem to have managed quite well on my own, with my patent brand of concentrate-lean-forward-squint-at-too-small-font-whilst-tensing-back-and-shoulders working method. Bah.

Rob's comment:
The fancy phrase I used was 'ulnar deviation'. One of its meanings is a sort of motion that's particularly likely to cause pain if you repeat it often enough.