Google is now showing the average review ratings for restaurant listings when you overlay restaurant results in Google Maps. This is currently working for me in the mobile user interface but not the desktop user interface.
Here is a screen shot of NYC restaurants in the map view of Google Maps on my iPhone:
Tim Capper noticed this on Friday and shared this news on Twitter.
Before this, Google just shows map pins without much information outside of the name of the restaurant.
Forum discussion at Twitter.