New Back-Gesture Discovered
First, this only works in Nagivation Apps, where you normally have to tap the back button in the top left corner to go back.
To do it is very simple, and I'm surprised I haven't seen anything about it. All you do is swipe left on the navigation bar title (make sure to start in the middle). For example, when in the Contacts app, select a contact. Then, swipe to the left on the bar that says "Info", starting in the middle. It will take you back to the list of contacts.
Another back-gesture to do is when you are in the iPod app. Select a song to play, and it will take you to the screen with the album artwork and iPod controls. If you have lyrics, make sure the controls are HIDDEN, then swipe to the right on the Album artwork. It will take you back to Song list.