From Mladen Djakovic on Get Satisfaction:
I would like to be able to zoom in and out by holding a key (e.g. alt or cmd) and scroll with the mouse. Am I really the first one requesting this? Couldn't find it in the topics.
Hi Mladen - no you are not the first person to ask for this but it is currently not high on our priority list.
With trackpads and magic mouse this works but with normal mice we would need to add a modifier as there is no standard way in OS X to do zooming with the scroll wheel.
I have added your request to our features list, but can't give any promises when this will be available.
All the best