In 2010 Google introduced Hotpot which is a recommendation engine that allows people find new places when they search. Hotpot basically allows you to rate and review the places you know, add friends whose recommendations you can trust.

After the initial release Google created Hotpot mobile apps which eventually led to the integrations of Hotpot into Google Maps as well as the mainstream Hotpot is now part of the core local search algorithm through Google Places.  An official statement by Google says the following:

Rolling Hotpot into Google Places helps simplify the connection between the places that are rated and reviewed and the more than 50 million places that already have an online presence through Google Places—places that millions of people search for and find every day on Google.”