I have slight carpel tunnel in my right hand, and it hurts a bit, so I s'pose that may be another reason I find it annoying. Some nights it's ok. Some not. Also, when I use the mouse excessively, I tend to get a bit of shake. >sigh< getting older...
I've been using computers since the zx81, so my muscles in my wrists have held up to quite a bit of abuse.