A Google search for hotels brings up hotel results in Google Maps. When you click on a hotel listing, it will show you a ton of information, including the reviews. The reviews come from Google but now there is also an additional section that shows you reviews from third-party web sites including Booking.com, Priceline, Agoda and more.
Brad Brewer, who tracks this stuff closely, posted about it on Google+. He said "Google now displays deep-linked reviews from the around web. The review sites appear to be limited to Booking.com, Priceline, Agoda, and for the first time 3rd party platforms ...no Expedia or TripAdvisor. This suggests TrustYou is the primary data provider, with platforms like Bazaarvoice powering 3rd party sites from Marriott to Starwood and IHG reviews."
Here are some photos showing this in action:
Forum discussion at Google+.