Best...Pointing...Device....Ever!
In all seriousness, I remember seeing a "preview" in a computing magazine when Logitech first announced them and I thought it was the most bizarre device I ever saw... I initially didn't want anything to do with it.
Then one day I was I office depot and they had one you could "try out"... and I really liked the feel. The large finger operated ball, the "window" that allows you to use your thumb to fine tune it, 3 buttons (well 4, but you know what I mean). When I bought mine "laser" mice where really uncommon and the trackball didn't "slow down" or "rumble" like a tranditionly ball-based mouse would. It was great, accurate, ergonomic.
I still have one at home, but I mostly use a laptop these days.. and it's getting harder and harder to find PS2 connectors on computers. I've replaced mine at work with the newer "cordless" model, but frankly it's just not as good... the USB connection is nice and all, but I have <b>NEVER</b> understood why someone would need a "wireless" trackball.. it's not like it goes anywhere... and you have the added cost of feeding the thing batteries...
I really REALLY wish logitech would bring back the FX... update it with a scroll wheel and USB support... I would buy 10.