Somehow my iphoto is broken since the ML upgrade. Do you have the same problems. I cannot swipe back/forth between pictures. Sometimes the gesture stops working everywhere so I unchecked it in trackpad prefs and rechecked it. It works in all other apps like Chrome, Pathfinder. Not in iTunes. So I used BTT to map the gesture to the cursor keys. I am quite sure that I remember that when opening an event a page back swipe got me back to the event overview page, which the cursor left/right obviously do not. Nor can I find any other short cut like CMD+[ to go back. Using BTT and mapping 3 finger swipe back also does nothing. At least knowing such a keyboard short cut would be nice. It is weird. I manage most of my gestures with BTT(0.785) because I think that the defaults are both stupid and not enough. The simple swipes though are just enabled in the normal trackpad prefs. Same setup I had in SL too.