Scroll Reverser for Mac OS X
pilotmoon.com
pilotmoon.com
I sometimes use a friend's iPad, but it is easier for me to keep alert enough to remember the difference between the way the iPad scrolls and the way vanilla Snow Leopard scrolls than to give up the ease of flexing rather than extending as described in the previous paragraph. The trade-off might go the other way if I was using the MacBook's TrackPad rather than an external mouse with a scroll wheel.
ADDED. In other words, if you use an external mouse with a scroll wheel instead of an Apple TrackPad, it is more likely than not that you do not want Scroll Reverser.
OK, good to know. The Scroll Reverser app does not, though.
This at least addresses the issue for the other Mac in my home that is stuck on Snow Leopard.
With this script:
WheelDown::WheelUp
WheelUp::WheelDown