I have a marked preference for trackballs due to wrist problems, and I use the Kensington Orbit at work. While it is far superior to any mouse I've ever encountered, I do slightly prefer the trackball I use at home - the Logitech Marble Mouse.
The design of the Orbit is suitable for any size hand, which is good since mine are quite small. Compared to other trackball models I've used, the ball on the Orbit moves relatively slowly (still far outstrips a mouse anytime!). The design of the ball area itself is such that it allows an inordinate amount of dust and dirt to accumulate in the internal mechanisms. The optical sensors on the inside of the ball cavity can be difficult to keep clean - I've found that the only tool that can do a respectable job of cleaning it is a straight pin, which is hardly a precision tool. But, as arduous as cleaning these sensors can be, it's very necessary because dirty sensors can seriously impair the function of the ball.
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