I got an email from Dave Lorenzini of Earthviewer today. He'd seen my articles on the open GIS consortium and grid sensors. In my Open GIS article, I'd said:

I think its interesting to compare this with Earthviewer. In my opinion, Earthviewer has one real advantage vis a vis other GIS tools: their user interface.

David confirmed that the goal of Earthviewer is to work with all of this GIS data and sensor information and provide the user interface to the data. They shine there and I haven't seen any other tool that does what Earthviewer can. Earthviewer has recently upgraded their data set to include 1m resolution data over the US and some very high resolution data for major US cities.