I think you’re right Daniel, I completely disagree with Jeff on the scrolling. I can think of more instances where I’ve intended to use the scroll feature and accidentally opened another tab than vice-versa.
I find the panning ability a very useful feature, especially since it provides combined vertical and horizontal scrolling (which makes it perfect for viewing large images), and the extra speed control it gives you is a godsend in long documents (instead of spinning the scroll wheel half a dozen times).
Additionally, considering that it is actually part of the scroll wheel surely it makes more sense conceptually that it would be linked to this sort of behaviour and another key combo such as R+L mouse buttons combined would open a new tab?