Google Building Maker has arrived, making it almost stupidly simple for people to contribute to the growing 3D buildings on Google Earth. More info on the Lat Long Blog as well, including a demo video.
BTW, they've made it fun, as I can personally say I just lost about an hour of productivity creating a couple of buildings over in the West Vancouver area. Definitely you need some SketchUp experience if you want to refine your buildings to be more than blocks or triangles (however, this is a great way to crowdsource all the square and triangular buildings that need to be created!).