First off the speed bumps, you get 2.1GHz from the base model, and 2.4GHz in the mid-range white and top-range black models. In the black model, you also get a 250GB hard drive, which is a BTO option in the other two. You can also spec up to 4GB of RAM, but this is often a lot cheaper to do after the event from a third party manufacturer (like Crucial). Everything else reads the same, even the graphic card is not a beefier offering. The only other performance enhancing addition, is 3MB of Level 2 cache.
So the good bits are the extra speed and the massive 250GB hard drive option (unless you have a black version). The bad bits, which will be talked about a lot more, is the lack of multi-touch. Apple have this technology and it would be so much nicer if they offered it too the whole range, but I guess that would hurt MacBook Air sales too much, so they will probably wait until a further revision before the MacBook gets this.