My wife bought me the Kensington trackball/mouse for Christmas. In general, I like it. Its size and shape takes some getting used to after using the Logitech marble mouse. It is Bluetooth. So, no wires to get in the way. And, it is small enough to fit in your shirt pocket. Also, it is switchable from mouse mode to trackball mode. In mouse mode, the ball is used as a scroll wheel; left, right, up, down. Neat! But, it is pricey.
I am having some problems with it when it comes to reconnecting after the computer wakes from sleep mode (suspend?). It happens randomly and is a minor irritation as it is pretty easy to reconnect it by running setup in "Blueman". But, I wish I could find a way to correct this. Has anyone else had this problem with Bluetooth devices?