(nod)
PB - I've tried using trackballs in the past and quickly realised they weren't for me. I've got far more control over a mouse.
Coincidentally, I've got one of
these on my desk at the moment after someone with RSI brought it back to us having decided it wasn't helping her. I've had a go with it and I'm not sure I'm using it correctly, would you use one or two fingers on the ball? My hand comfortably fits with my index and middle fingers over the ball leaving the ring and thumb for the left and right click. I guess having two fingers on the ball helps with stability, but without using it for a length of time to get used to things I don't know if it's more precise.
O'course, and as with any type of ergonomics, it's down to personal preference. You can get used to anything given enough time.
If desk space is at a premium, could you not just get a bigger desk?
:D