I've got two Logitechs - an older cordless ball-type mouse at work and a cordless optical mouse at home, and both are wonderful. The one at work still requires removing the ball and cleaning the gunk from time to time, but it's still head and shoulders above any regular mouse I've ever used. It's almost four years old and I've never had any trouble with it. The optical Logitech at home is even better. Both are amazingly comfortable and well built.
The one feature I CANNOT live without is a thumb button. I've assigned the thumb button on both mice to act as the CTRL key (CMD for you Mac folks), and this speeds up shortcuts and combined keystrokes by a factor of 10. If you've never tried it, give it a shot. You'll never look back.
