i was a big fan of the trackwheel, also. After using an 8100 a couple of weeks, I was not convinced the trackball was better. Well it is. Having the bidirectional movement of the trackball is much more dimensional that the one way only movement of the trackwheel.
I'm new to BB but have two, a curve that I use daily and an 8707 that is 'spare' - the curve has the trackball and it's very easy to use and multi-directional ... the 8707 has a thumbwheel and I don't find it so good at all.
Prior to owning an 8830, I only had experience with the older 7520's and 7250's (and 957's...I think that was the model number..) and the scrollwheel. Although the scrollwheel was a good idea in it's time and definitely served it's purpose, the trackball is far superior. It will only take a short while before you think how you ever got along without it!!
I'm a thumbwheel guy. That was my favorite imput device ever for the Blackberry. I've gotten used to the trackball on my Curve and 8800 but I'd trade 'em in a heartbeat for the trusty old thumbwheel. Maybe the users that go fast and furious with emails all day get "numbthumb" from the wheel, but I'm not a power user so it never happened to me. Perhaps I'd feel different if it did happen to me.