Take any used car and tune it up, put new tires and brake systems on it, and rebuild the engine and transmission. When you are done it will feel like a new car even though it looks the same. This is what Apple has done with Snow Leopard: Functionally, it is the same OS as we've all seen in Leopard besides a few new features, but under the hood things have been optimized to a great extent. While this has been discussed in great lengths by Apple and on Mac news sites, it is one thing to read about it and another thing to experience it in person.
