I believe they have Street View backpacks. Not sure of the specifics, but if I remember correctly you can walk around with the backpack and take pictures of places that cars can't get to and have them added to the map.

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...

This may go some way to an explanation:

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

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?

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