If anyone's curious about an example, Mall of America is one of the locations mapped with this feature, here's the Google blog post: http://googleblog.blogspot.com/2011/11/new-frontier-for-goog...

It's a pretty interesting development for me to watch as the app I'm currently working on named Mashupforge (http://mashupforge.com) lets people easily create interactive maps out of image floorplans.