We use R and Shiny server pro for our back-end. It's hosted on AWS EB with our static site on S3. We love it - the data scientists can write and push features directly, and everything (including our API's) are easily maintainable in R. I've been shouting the praise of R and it's usefulness as a production ready language for a long time. Contact me with questions about data science, start ups, or R - if you have a dat…
Personally if I wanted to use R I could just interface with it from another language (Python, .Net, Java etc.) I haven't played enough with R recently to make an informed opinion on the current quality of its network libs and framework stack however it seems like an interesting gamble (that's paying off for you all?) given where the focus of the R community has been (statistical programming rather than general use) and statements on the front page of "No web development skills are required."