I thought of this thread the other day when I was out getting some exercise and decided to use Google Maps to determine the shortest way back to the house.
I pulled out my Nexus 6P and opened Google Maps and verified that the route I had taken was also the shortest route back. As I was about to put the Nexus back in my pocket I noticed there was an indication on the screen showing that I could arrive at my destination in only 9 minutes - it was an ad for Uber.
I thought it was a great example of ad placement - if I had been too tied to walk back it would have been easy to take Uber knowing that it would only take about 9 minutes and the fare would be between $6 and $9.
Here's a screenshot: