MacOS – Using three-finger drag and three-finger back on browser

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

IDK about the Magic Mouse but three finger swiping works on the Magic Trackpad

By default swiping between pages is set to two fingers in Lion. However chrome doesn't currently recognize two finger swiping but it does recognize three finger swiping.

To enable three finger back and forward swiping simply go to the Magic Trackpad preferences and set "Swipe between Pages" to "Swipe left or right with three fingers".

Update

Google has updated Chrome to work with a one finger swipe for the Magic Mouse and a two finger swipe for the Magic Trackpad in Lion.