Our entire back-end is built in R, mostly within the Hadly-verse, and we use Shiny [2] as our web framework.
Our team works a bit differently than most, I suspect; our data-scientists build features and analysis directly in R, and then add the functionality to our Shiny Platform. Our "real devs" are all server + DB, or Android guys. This has created a great development system where all of the "cool findings" and 'awesome visualizations' are immediately implemented in our system, and made available for our clients!
[1] www.Gastrograph.com [2] http://shiny.rstudio.com/
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Edited to add; R is a great language and is 100% suitable for production systems. Its older than Python(!), and, with some experience, can be made in to high performance code.