Neither captures the distribution of usage from small- to large-scale apps, but it does look like the community has already moved both in mindshare and number of production deployments. I'd wager that Heroku's PostgreSQL default is responsible for much of that.
In October 2013, NewRelic reported that 53% of their customers are using PostgreSQL: http://blog.newrelic.com/2013/10/10/infographic-state-stack-...
In July 2014, Planet Argon's Rails survey showed a surge in preference for PostgreSQL since 2012: http://rails-hosting.com/Results/2014/index.html#Database
Neither captures the distribution of usage from small- to large-scale apps, but it does look like the community has already moved both in mindshare and number of production deployments. I'd wager that Heroku's PostgreSQL default is responsible for much of that.