Hi there,
cause I’m interested in the 3D usage of OSM (but not an active developer on this topic) I had contact with some of the related projects. Cause I see a good possibility to cooperate on central problems, I was asked to get all the projects together:
http://wiki.openstreetmap.org/wiki/3D_Development
This might become more important due to the massive grow of buildings caused by Bing aerial photography.