I managed to set R up and use it with Tableau. It does involve some acrobatics, but it isn't a rocket science.
The hard part is to write working scripts, given that in most cases you don't get to see the shape of the data that will be passed to R, and you'll have to imagine what it looks like.
Thanks Dimitri, are you running it on Windows?
R runs on the same desktop PC as Tableau, on Windows 7.
Thanks for the comments and hopefully the feedback from Dimitri was useful - I think it was.
Something extra to consider is more information on what you plan to do with R ?
If you are just running it as a 1-off on your own machine, then that is fine, yet if you want to throw it to a Tableau Server, then you could deploy it differently.
Something to consider is if you were building for scale - you might want to consider putting it on R Studio or Shiny for R-Studio and render it into Tableau.
I installed R and got it working on my machine, and faced some challenges when looking to scale it. I then threw R out the window and just rebuilt the solution a different way. It was involving maps and network diagrams in my case.