<< i use an intellimouse explorer 3.0 because I game, I also have a MS natural pro keyboard. >>
I used the Logitech Trackman Marble+ for a while and I just couldn't get the hang of it. My thumb would just get too tired, and when it came down to doing some photo editing, and other tasts that required drag and drop, it was just a pain to work with.
Since then I picked up a Microsoft intellimouse Explorer 3.0. Definite improvement! Though, I believe that my Logitech Optical Mouse feels sturdier, and fits the hand a bit better, but I decided to get a mouse touted as being one of the best optical mice.