Rob Conery has a post about how they run Tekpub using NoSQL that’s a great read.
I’m not qualified to talk about Ruby code but that part is kind of irrelevant. He hits all the right notes in talking about why they did the things they did (I could quibble about the cost ‘criticism’ of , but that’s a business decision), especially in terms of separating reporting.
It’s a good read, check it out.