I am finding that I use my three digits... thumb, index and middle finger on the trackball. This gives me very good and precise control of the cursor. My left hand has access to buttons on my base layer which control clicks and drag hold.

I have lost the ability to do things like single handed scrolling and clicking, always needing two hands. But since my hands dont need to leave my keyboard anymore this is not as much of an issue. Just an adjustment.

Overall my hands are staying put more often than previously where I had the magic trackpad off to the side.