It looks like Microsoft and Google are accessing the exact same pictures. My mom was visiting a friend, waiting for me to arrive home from a trip on June 13, 2002. Her car is visable in the picture that shows that apartment building on both of those services as well as the original terraserver.microsoft.com which has been up for several years.

The MSN virtual earth service zooms in the tightest. Terraserver was second, slightly less using the same picture, just not stretched as much. The free Google was quite a bit less, the premium one will probably go to the same point as the Microsquish ones.

I then tested a place in Kenya I know well. Terraserver and Google didn't even go there, but MSN virtual earth did. I couldn't even come close to the town I wanted to see there though. The clear winner there was NASA's World Wind http://worldwind.arc.nasa.gov/ Too bad it doesn't match the other ones in the US.

Have fun exploring the world.