As you are aware, Google Earth new Beta is using COLLADA for its 3D models. You can drag and drop COLLADA .dae documents on the earth. The models are then packed in a .kmz file, which is a zip file containing the dae file, the textures, and other information.
Google Sketchup has also been updated to support Google Earth, and can be used to create .kmz files when exporting to Google Earth. It does not export directly to COLLADA, but the .kmz file contain a .dae COLLADA file if you unzip it. There are many models available on the 3D warehouse site, that can be saved in this new .kmz format by SketchUp, and since both SketchUp and Warehouse 3D are free, this has raised a lot of interest amongst COLLADA users.
The only issue is that the current implementation is not conformant to the specification, it is still in beta though, so will probably be fixed soon. In the mean time, we have posted a KMZ conditonner on sourceforge, which can be used to create conformant 1.4.1 files from the .kmz files.