Google has formally announced what Joy and I had ferreted out several weeks ago: They are now showing your Google Local reviews with your Adwords ads IF you are using Location Extensions and have the requisite star ratings (3.5 minimum) and number of reviews (not sure what that number is).
*Location extensions can now show ratings from local Google My Business listings *
Last year we made it easier to manage location extensions by automatically linking your Google My Business location information to your AdWords accounts (http://goo.gl/e8Mnby). Starting today, ratings from your Google My Business listings are eligible to appear in ads with location extensions enabled on desktop and tablet. People increasingly rely on the opinions and experiences of others to help make decisions like which pizza parlor to visit, where to get your tires rotated or which dentist to make an appointment with. Local ratings make your ads more useful to consumers searching for local information, and can improve your ad performance. To showcase your Google My Business reviews in your ads, make sure to have location extensions enabled in your account. Learn more (https://goo.gl/zuUWZt)