I think I had the same reservations around the ball vs. wheel issue.
Mainly, because when composing a letter, i need to move my thumb off the keyboard to scroll down from the To: to Subj: to body. Also for selecting items within the To: drop box as my addressbook gets filtered.
With the wheel, I could scroll with my index finger while typing with thumbs. Felt more efficient.
Also, i feel like the ball will "click" but not move sometimes. I figure this might be because I'm rolling diagonally - and so it isn't clear which way to scroll. So to get across the 5 icons in my homepage menu, it takes me two swipes across instead of the one swipe I'd like. Or wrap around might be nice.
Still, i wanted a phone with a camera (2 year old boy!) that was a blackberry with a full keyboard, so this is the situation I'll adapt too. 8700 with camera would be my preference, but I understand the need to satisfy more of the "consumer" market.