When using any recent MacBook Pro or MacBook with Photoshop CS5 you may notice a huge annoyance of accidental canvas rotation.
The culprit is that Photoshop now accepts multitouch gestures. Overall, these can be a great addition to your workflow. But in certain situations it can cause a real annoyance since our normal undo (⌘Z) does not fix the problem (since this only a change in view and not a change in the actual document). Adobe has placed a “fix” on their website which disables all trackpad gestures. However, this also will disable the pinch-to-zoom multitouch gesture and others that are sometimes useful.
If you want to keep pinch-to-zoom but disable the canvas rotation you need to do so in [System Preferences > Trackpad]. Simply uncheck “rotate”.
Note: this requires 10.6.2 or higher (anything lower than that and your still screwed! : )