Apple recently bought them. Seems they use image based rendering, not polygons. Looks better than google, they claim accuracy of one foot.
What could be better than Google Maps? C3 Technologies' stunning 3D city displays, which let you rotate, zoom and pan through the city as if you'd modeled it all on your computer. The technology, which uses footage captured from airplanes and processed through a formerly proprietary military missile-guidance system, absolutely must be seen to be believed. Check out San Francisco, starting around 2:00: