If you want to see where Google is Headed with its combination of Google Earth and Google Sketchup have a look at The joint efforts of two (small) swiss companies: viewtec and cybercity as well as a german one RSS
Especially viewtec provides a full range of solutions for the 3d visualization of the world ranging from the acquisition of basic data to the efficient generation of 3d-City and Megacity models and the efficient streaming of these models over the web (unfortunately only ActiveX right now).
Cybercity and RSS (Remote Sensing Solutions, not what you have thought.) are generating 3D-Models from stereogrammetry images, hence (semi-automating) the manual process used right now by Google Earth.
Have a look at the webstreaming solution TerraViewWeb yourself.
Google has released a beta version of Google Earth 4 as well as Google Sketchup. Not only does Google Earth come in localised versions and is available for Linux (were earlier versions of Google Earth available for Linux?).
GE4 also has a leaner user interface. Personally i think that the old UI especially for rotating was easier too use, but maybe i just got accustomed to it. It also supports the “streaming” of .kml files etc.
But the most important change is that it now supports textures on 3d models. This clearly shows the direction Google is taking with this tandem fo GE4 and GS. Textures can be used to do “photorealistic” renderings of houses etc. Textures, “quelle surprise”, are also the key ingredient for putting virtual ads onto/into buildings and other 3d structures.
Textures are also essential for the ability to do virtual walkthroughs of museums etc. which i think will follow suite. I haven’t tested it, but i think, giving its origin, Sketchup is already able to produce such models.