They have the Google Street View Trekker program[0] where they have the backpacks similar to the units mounted on their Street View cars. They tend to do "tourist attraction" type areas like monuments, parks, and so forth.

[0] http://www.google.com/maps/about/partners/streetview/trekker...

I wonder if this will be the next step for them; mapping all indoor and outdoor locations, integrating relevant ads into the street view of certain stores?

This may go some way to an explanation:

http://randomstreetview.com/#rrrxi_91xj4_-1g_0_-19

You can see their Street View stuff at the Computer History Museum in Mountain View.