Using a mouse for work all day doesn't have to be a recipe for carpal tunnel syndrome. If pain comes with the territory, you're probably using your mouse incorrectly.
A slight twist of your wrist can cause a serious problem, but Vivienne Fliescher (writing for Performance Based Ergonomics) suggests a fix:
Get off your wrist rest, lie your mouse on something flat like a mouse pad and move your whole hand and arm together, relax the grip on your mouse and voila, you'll be on your way to being pain free and avoid future troubles.
Vivienne says it will feel a little awkward at first, but after a few days you'll adjust and have a pain-free way of using your mouse. For more information, check our her full post and our guide to ergonomically optimising your workspace.