Google has updated Maps for Android to version 6.0, and has been released into the wild that is the Android Market in the U.S. and Japan today. Included with it is retail and airport floor plans for indoor navigation.
The indoor maps aren't as good as the outdoor navigation, so there's no turn-by-turn navigation, but it does provide layouts for the nearest shops, bathroom or elevator. The information is pulled from the same spot it is now "My Location", but it has been optimized to detect movement along the z-axis.
Included, is a feature called "Automatic Floor Detection" that can tell if you're in an escalator or not, so it knows what floor you're on. Google does have plans to extend the features with the indoor layouts, opening up its mapping inventory with a self-service tool (which is currently in beta) that will allow business owners to upload floor plans directly to Maps.