In terms of shape and usability, the mighty mouse is fine, in my opinion. I do get a little sore at times when I'm doing some 'mouse intensive' work, like photoshop or something, but nothing too serious. What I hate about the mouse is the scroll ball. It's just the biggest headache to clean. I've taken to cutting up thin strips of sticky tape and slowly rolling them under the ball to get the damned thing workable. I would not recommend a mighty mouse.
This Kensington slimblade trackball looks pretty cool! ... the reviews don't sound so great though
This Kensington slimblade trackball looks pretty cool! ... the reviews don't sound so great though