Thanks so much for posting this. I love seeing quick examples of great TDD minds working on things that I can easily wrap my mind around.
One quick thing: Google Reader (on Chrome) doesn't pick up the Gists, and it took me a little while to realize that stuff was missing. I don't know if this is a known issue or not, I just figured you'd want to know if you don't already.
Anyways, thanks again! I hope you post more examples like this in the future.