Google has been "letting" people map for awhile now. A good idea in theory but I am not sure if they are not just using the people as some sort of free work force to get 3D architecture into the map.
And most of the maps aren't really all that good, i.e. most of the structures are never really complete or accurate.
It would take a bunch of "real" mappers to complete this project the right way. I think they should be a little more strict on the entry policy. I use google earth alot and I don't want to see some cheesey building when I am trying to look for something important.
I guess all is free so I can't complain but so much.
Now, the 3D warehouse is a completely different story. Haven't actually tried to convert anything from there yet. Well, I don't use the new source engine as much as I should.
http://sketchup.google.com/3dwarehouse/