3D building data is only part of this, arguably the least interesting part. It'll be interactive and 'living', not much unlike city-strategy games. It'll also act as a real-time data view of cities in ways that aren't available on the Web yet.
Sure, it's basically a 3d visualisation of real life cities using the latest Web technologies. Part data visualisation, part game, part art – it's ambitious and will be an interesting view of the cities we live in.