Automated route following. Arbitrary image display. Coordinating Google Maps with realtime GPS data from elsewhere (the proof of concept is the Seattle realtime 911 registry). Loading map locations directly. Generally exploring the web app in immense detail.
I'm amazed. And not just at the technical sweetness of this set of hacks -- also at its presentation (the author releases early and often, and maintains page history) and at the simple fact that it's possible. If I were a clueless marketing dork, or a boneheaded oldschool software guy, I'd be crapping my pants at what it's possible for interested people to do, in public, to my wonderful client-side web creations.
Good thing I'm not either of those people.
This is one of those HOLY SHIT moments for me.