If one knows the fundamental design of OKCupid one knows that these guys are sharp. The did their web app entirely in-house using what they claim as 'superior language, code, and framework.'
On one of their job listings they list these technologies: "Ruby, Python, Clojure, Javascript, CoffeeScript, Backbone, HAML, SASS, Rails, Sinatra, Hadoop, MongoDB, Redis, Heroku, AWS, and more"
It does seem like it runs pretty well, and they have a sense of humor at every corner.