It's in a browser and works--Google has a nice plug-in for GoogleEarth and it can be used to make 3D tours. Check some nice work from Prad at the Acropolis and also Rome.  Further, it is a mash-up of flickr pool photos that you can see when you click the HK icons.

So you just gotta wonder when someone will make a more realistic virtual world that can also be in a browser. Or is that even really the right objective?

If a 3D online space could work as nicely as the Google Earth plug-in then it would certainly be worthwhile.