It won't take long to fully appreciate the trackpad. The trackball was easily subjected to dirt, etc, which caused occasional glitches and made cleaning necessary. The trackpad doesn't have that issue and is a pleasure to use. Posted via BlackBerryForums.com Mobile
I admit that I miss the trackball myself, but after nearly two years with my 9700 I got the feel of the trackpad and I have adapted perfectly well. I think the idea of the trackpad is to save replacement from dirt and oil buildup under the trackball, but I know many people who used the heck out of their 8900's and still have no problems with it after several years. Furthermore, after a short time with a new trackpad it has a tendency to recess on one corner or another, and it would have a slightly crooked look. The good old paper tape trick can fix that, though it is another topic. Overall, the trackpad is great to use and easy to adapt to.
Trackpad is way better IMO. I think they went with this A) because of the dust issue around the trackball and B) to get to something a little like a lot of the "touch" phones. I got used to it in a day. It may be the best hardware update RIM ever did.