While I have your attention... is the 3" model mouse hackable in your estimation? Or a separate specialized interface required, like the optipac or the USB one you used?
Thanks again,
rampy
The 3" is hackable, but you have to open the case to get at the optical circuits, and note what OSCAR said about some problems. Others have hacked the wico 3", though. The happs 3" looks easier to hack because the circuit boards are accessable from the outside. Then again, you could use the optipac or the happs USB interface instead of mouse hacking if you don't mind spending $$.

is there a recommended version of the 2 1/4" trackball for MAME cabinet folks?
My first trackball was a Kensington Expert Mouse Pro. I still use it for normal windows stuff. It is good, but the cost was $100 US, so you can buy the arcade ones for cheeper. The expert has nice ball bearing rollers, pretty good at continuing a spinning, and a very high ball stance. Some cool things about the expert is that it is USB, and the ball can be switched with billard balls (like all 2 1/4"s). The ball is free to be popped out, though, and the case is shaped so it would be some work to get is mounted under a control panel, and it needs the whole circuit board to work because of using reflection for the opticals instead of the standard wheels. So it would be great for trackball window/mac use and part-time mame trackballing, but not the best for a control panel, IMO.
After playing with the 3" trackball, I'm going to stick with the 3" for maming. I love the feel and spin of the 3" much better than the kensington and wico/suzo 2 1/4 inchers. I really should test the wico 2 1/4 some after tuning it, but I can't see using it instead of the 3" after seeing how much better it is.. Except if/when I make a cocktail cab.

just my 2 cents.