During the CS4 development cycle, the Photoshop and Bridge teams worked closely with Apple* to support the multitouch gestures supported on MacBook Air and newer MacBook Pro systems. As a result you can zoom and rotate documents using three-finger combinations.
The rub is that especially on the latest systems (with the enormous trackpads), it can be too easy to zoom or rotate accidentally. Unfortunately Photoshop doesn’t ship with a preference that would govern the behavior. Therefore we’ve released an optional plug-in that will disable zooming and rotating via the keyboard if you’d like. Just drop it into your Plug-Ins folder, restart Photoshop, and you’ll be set.
* Next time you hear someone start in with a bunch of “Adobe doesn’t care about the Mac” crap, I’d like you to think of this. People here go the extra mile because they do care. Deeply.