Four-finger swiping on multi-touch trackpads have a few interesting behaviors not shown in the Trackpad System Preferences panel.
As documented, a four-finger down swipe executes Exposé, while a four-finger up swipe shows the desktop. Without any intermediate steps, a four-finger swipe (up or down) will bring the windows back to their prior locations. The System Preferences window makes it appear as though after swiping up, the user must swipe down to return to a normal view, and after swiping down, the user must swipe up to exit Exposé.
However, when using Exposé, it is possible to scroll through the Exposéd windows using two-finger scrolling in any direction. Then a four-finger swipe up or down can be used to select the highlighted window as the new frontmost window.
With Spaces active (i.e. more than one Space being shown), two fingers can highlight different spaces. A four-finger down swipe activates Exposé within the Spaces; a four-finger up swipe whisks the desktop to the selected Space and shows only the desktop. A four-finger left or right swipe switches to the selected Space and opens the application switcher overlay.
A four-finger left or right swipe opens the application switcher overlay. Two finger scrolling then highlights different applications. A four-finger tap then selects the application. (That is the hint I'm most proud of; the system will recognize up to a four-finger tap!) This happens whether the option for "tap to click" is on or off. Also, four-finger swiping in any direction while the application switcher overlay is open takes precedent. A down swipe will activate Exposé and the application switcher overlay will disappear.
Pinching in any location where icons are present (desktop, icon view in Finder) works just like the user would expect. A pinch makes the icons smaller, and a reverse pinch makes the icons bigger. This only works with Finder as the active application. Reverse pinching in QuickTime activates full screen mode. Pinching during full screen returns to the last screen size. Pinching in Mail affects text in messages as expected.
Three finger swipes only work if the application is the active application, and if the pointer is inside of the application window. Three finger swiping in Mail, up and down, moves the selection from the current email up or down once, respectively. (This also works in Address Book, but only in the Contacts column.)
Three finger swiping in Finder activates the backwards and forwards buttons like it does in Safari. (This also works in iCal, but will move forwards or backwards one day/week/month, depending on the direction of the swipe and the current view.)
Oddly, no finger gestures work in iTunes, other than two finger scrolling. Videos can not enter full screen by reverse pinching. Three finger swiping won't select the next song. Pinching and reverse pinching don't change the text size.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20081030215945667