A number of people have reported discomfort when holding the redesigned Apple mouse that ships with iMac, blue G3 and G4 desktop computers.
Most people hold a mouse between their thumb and fingertips.
If you hold the new Apple mouse this way, you're probably experiencing hand discomfort after a while. This is especially a problem for people with large hands. Furthermore, many people complain that it is easy to lose track of which direction the mouse is pointing. If you're willing to re-train your movements, however, there is a possible solution. When used as designed, the Apple mouse can be quite comfortable.