I had some problems before when I had a regular mouse. But no problems since I got a Microsoft Optical Trackball.
My hands also got cold before. But I also solved that problem by lowering the keyboard (or raising the chair) couple of inches. Also make sure that you don't have a lot of weight on your elbows (cuts off circulation).
Only time when my hands get a little stiff now is when I work 48h days, but I wouldn't expect anything else
