One of these now sits on top of my TI2.
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I set the scroll ring(it's around the trackball) resolution really high and use it when hovering over parameters in VC. It's like a data entry knob. It will also work on all parameters in your DAW that respond to a mouse's scroll wheel.
Good Link! More devices like this?
There are a bunch of different trackball mice available. I liked this one best because of that ring. You can also program the buttons to perform custom key combinations. At the moment I have nothing assigned but I have used copy and paste in the past.