A Quick Tour of the MacBook Air - 3 Fingers For Back (
Page 8 of 11 )

Also with the touch technology is the ability to use 3 fingers for
moving back or forward in your browser (Safari only in our quick tests,
but at least the scrolling up / down with 2 fingers works in all
browsers).
You accomplish this by moving your 3 fingers either to the left or
right on the touch pad. Pretty cool. Notice the keyboard. Remember it can be backlit when you need it.
Business Advantage: Browsing has never been easier; No need for a mouse.
Business Drawback: Safari only is lame, but I get it. Oh, browser wars.