We at RStudio are actually working on a hosted version of Shiny which may be of interest. We have modeled it after the Heroku model, but obviously very much tailored towards hosting R sessions. If you would like to be part of the early alpha please sign up here: http://shinyapps.io/ and we will reach out as soon as it is ready for some people to bang on it and give us feedback.

There's actually a chap on the mailing list who is from heroku and helping to make changes to allow it to run as in a worker. Not sure whether it's working yet, but the blocker was that shiny required root, but the devs have released a patch which fixes this.