The thing that worried me most about going from my Treo 680 to my first BlackBerry (8300) was the trackball. I tried the Pearl for an overnight session a while back...and for some reason, I detested the trackball then (among other things). So...I bought the 8300 with some degree of hesitation.
But...I have grown to love the trackball, which is suprising since I was a die-hard 5-way/d-pad guy for a long time...although I have no experience with the trackwheel (except on the Samsung Blackjack...and I disliked it on that device). It is quick and easy to use, and has been super reliable to me. My paticular phones trackball clicks decidedly, and gives great feedback...and I really like that. Overall...I am a convert. Pure and simple.