We just shipped a new product, promoted the hell out of it (with great results, thanks!), the site is getting huge traffic, but our server is as quiet as it was yesterday.
Because this web app uses no server resources. ;-)
That's the magic of HTML 5 local storage, and static pages on S3.
Thanks to the W3C and to Werner Vogels (for persisting in getting the ability to access the root of a domain from an S3 bucket). As a result, we get unlimited scaling with zero investment. Consider this an endorsement for both innovations.
Now, that said, in future incarnations, we will have a server component, and scaling will be an issue. But for right now we can bask in the glory. ;-)