I have a Kensington Trackball (the original grey square 4 button model) which works great and which I absolutely love. I have had it about 10 years now and it still works perfectly fine. Kensington got a lot of grief (and rightly so) for not providing driver support when migrating it from...
button mapping
compatibility
compatibility mode
dell
device recognition
driver support
feedback
hardware issues
installation issues
kensington
legacy hardware
mouseworks
softwarecapabilities
tech support
trackball
troubleshooting
user experience
windows 7
windows migration
windows vista
