If you have two-finger swipe between pages set then when you swipe in Safari you see a card-slide animation, and if you do the same in iCal month view you see the page tear animation. You can not swipe at all in some apps like Finder or System Preferences. However, if you set three-finger swipe between pages then when you swipe in Safari or iCal there is no animation (I much prefer this as everything suddenly feels snappier). Furthermore, with three-finger swipe you can now navigate back/forward in loads more apps... it works in Finder and System Preferences. I don't get why the behaviour is different, or why Apple isn't making it clear how different selections result in completely different behaviour. The fact that certain selections mean you can't swipe in a ton of apps should be made clear... if I hadn't chanced to try three-finger swipe I probably would have just assumed that swiping in Finder wasn't possible anymore.