How can I swipe with three fingers to go back and forth in my history while browsing?
I looked into it and here is what I found.
In Lion the swipe to navigate is grouped in System Preference > Trackpad > More Gestures under the "Swipe between pages" option.
Under that option, you get
A) Scroll left or right with two fingers
B) Swipe left or right with three fingers
C) Swipe with two or three fingers

Option A is the new navigation method featured in the new Safari during the WWDC keynote.  It is the new feature in Lion.  You SCROLL left to go FORWARD, right to go BACKWARD. You get the cool page flipping effect with this but developers need to update their code to support this feature.

Option B is the original swipe to navigate method used in Snow Leopard after the introduction of the Magic Touch Pad.  You SWIPE left to go BACKWARD, right to go FORWARD.  Many cool apps support this feature only at this stage.

Option C is the best of both world.  Try to use it and play around in the new Safari... it is a bit confusing to navigate with both 2 fingers and 3 fingers swipes in the opposite directions :p