My experiences from writing + running our tasks App backend ( http://tomorrow.do/ ) on Heroku:

1. Node.js + expressjs is quite an efficient option for serving API and the static site on Heroku, only the single free dyno is needed for over 3 million installs and peaks of 30-40k site visits. Only rarely have we needed a second or third dyno under an extremely heavy peak traffic period.

2. A commercial CDN is a good and not too costly option for static files ( http://maxcdn.com )

3. AWS database + file services like DynamoDB/S3 are not that flexible but aren't too expensive, pretty much scale up and down without you doing too much and don't go offline much at all

whoa. he was not even using etags? wow. i thought aggressive caching is a given for any website expecting major traffic.

Obviously. All of this was dumb stuff I forgot to do. There's a lot that goes into building a product :)