I did a quick check for scrolling via mouse wheel in the Google Maps
API, and it's not something that is built in (as far as I can see).
On the Google Maps discussion list there is a recent thread [1]
discussing how you can "roll your own", but that is not something I'm
interested in doing right now. If someone else wanted to take it on
and provide a patch, though, that would be cool.
~wyatt