I found this Google Earth Network Link today on the Google Earth Forums:

Map Comparision Network Link

It allows you to navigate to a position in Google Earth and when you stop moving, creates a pushpin which has direct links to the same co-ordinates in Google Maps, Microsoft Virtual Earth and Yahoo maps.

I found it a very quick way to compare aerial map data, especially to see the date differences between the data for each provider. For example look at the business park below, there are obviously a good few months difference in date between the providers as half that buildings are missing on some.

 

 

Microsoft Virtual Earth

 

Google Maps

As you can see the Google Maps / Earth data is much more up to date, now if only they would get full UK coverage!