I set up my iCal prefs to view 24 hours in the Week view, and was happy until I wanted to change it to a more zoomed-in level. Having just stumbled upon the Firefox text zoom feature, I decided to try the same thing in iCal to Zoom the view, but, alas, it didn't work.
When I tried a different modifier, however, voila! Holding down the Option key while moving the scroll wheel up will zoom the viewable hours out (see more hours in a view), while scrolling down will zoom the viewable hours in (closer view of your calendar). This also works in Day view. Most excellent!
[robg adds: This handy timesaver saves a trip to the Preferences, as it sets the value for the "Show nn hours at a time" pop-up you'll find there.]

