The Heroku model is not ideal for commercial apps, it's good for very small apps, but if you scale up it's not cost effective at all. Things that would take a half-hour to setup with puppet on amazon become add-ons that you have to pay large ongoing fees for. Instead of investing in building out infrastructure optimized for your application where you have options on how to grow, you're shoe-horned into a one-size fits all model, that starts out cheap, but has a built-in premium which becomes more and more painful the larger you grow. We host our app on Engine Yard AppCloud which is considerably more open in that they give you access to the cloud "metal" but even there the clock is ticking to where it just makes more sense to hire a full-time systems engineer and build it out ourselves.
Don't get me wrong, I understand the value proposition of a highly tuned blackbox Rails stack, and there is certainly no faster way to get up and running. So it may become the place to be for early stage startups and prototypes. But the particular model that Heroku has is sort of like the Drupal of infrastructure: it's an amazing platform that has everything you need out of the box, but which also comes with a lot of baggage that can easily become an albatross when you are really trying to dial in a growing app.
Don't get me wrong, I understand the value proposition of a highly tuned blackbox Rails stack, and there is certainly no faster way to get up and running. So it may become the place to be for early stage startups and prototypes. But the particular model that Heroku has is sort of like the Drupal of infrastructure: it's an amazing platform that has everything you need out of the box, but which also comes with a lot of baggage that can easily become an albatross when you are really trying to dial in a growing app.