Prior to Mavericks, one could reverse the direction of a Magic Trackpad, using the following
defaults commands, and magic five-finger gesture to reorient.
defaults write com.apple.trackpad.orientation TrackpadOrientationMode 1 sudo defaults write com.apple.MultitouchSupport ForceAutoOrientation YES
NOTE: this is not the same as reversing the scroll direction. It completely reverses all input and gestures on trackpad.
UPDATE: I got it to work. Ray Shan's "reboot the trackpad" might be part of the magic. Also, five fingers + hard click seems to be crucial to activate.