when i bought this mouse, ibought it becuase of the ball-less mouse. i hated the wheel mouse in the sense i had to clean its rolers every week once a week. got tedious.
This one runs literally on any surface including your table, (apart from reflective surfaces like glass or mirrors)
even runs upside down!
the ergonomic design is important to me as i have heavy usage for the mouse.. and this one has been the best so far
with its two extra buttons to go back/foward on the net or on the machine (or you can set your own) i think these were very time consuming.
Overall, the first 2 weeks, the red light will bug you especially if you leave it on over night (the computer). you get used to it and then feel when yuo use someone elses mouse, how you wish the optical was on every computer!
Comes with USB or PS2 connecttions (adaptor) and has no problems with XP.