I just installed Snow Leopard on my June 2007 MacBook (a plastic one). I had my hopes up that Snow Leopard would bring MultiTouch, that's 3 and 4 finger gestures, to my old computer's Track Pad according to this Gizmodo Article - amongs many others.
Sadly the truth is that the new features are only given to MultiTouch track pads, the older Track Pads can apparently not handle more than two fingers on the surface at one time. This means that, pretty much, from the start of the MacBook Air and forward the laptops all have MultiTouch TrackPads. Mine doesn't. Read the "Multi-touch coming to older MacBooks? Not so fast."-article on Tuaw for a better and more precise explanation of the innards of this.
Bhlergh - still only letdown in Snow Leopard so far. It's still very cool! :)