Been using Kinesis Freestyle 2 Mac[1] & bluetooth variant along with a Kensington Trackball[2] for just over 3 years and I'll never go back. I switched keyboards one week and then switched to the trackball and started using my left hand for the mouse the next.

Overall it took a week to feel comfortable with each and another week after that to be back up to my previous typing / mousing abilities (the week where both were new was particularly amusing - I could barely highlight text at first). Now I can switch between standard keyboards and right or left handed mousing / trackball / trackpads with ease.

Background: At my last job I developed tendonitis in my wrist after some particularly grueling work weeks using the Apple wireless keyboard and trackpad. I think the trackpad is what really did it - the flexed position it encourages your wrist to be in really couldn't be ergonomically worse.

[1] - https://www.kinesis-ergo.com/shop/freestyle2-blue-mac/ [2] - http://www.amazon.com/Kensington-Orbit-Trackball-Mouse-Scrol...