[bergkampf]

Secondly, I'd like to know how many of the apps that Heroku hosts are actually production apps.

Agreed. Because of Heroku's unreasonable pricing, I see it as a feasible service only for staging and development. Without deep pockets, I would never want to host a potentially popular app on Heroku since I could never afford to scale it there. And because I don't want to have to go to the trouble of reengineering something after it's been developed to move it elsewhere, I would rather build it elsewhere from the start.

[andrewvc]

What about how heroku is designed would require re-engineering if you move it elsewhere?

Rails + SQL + Memcached = the most standard stack you can build, aside from the fact that they use Postgres. Most of the addons aren't too hard to setup oneself either.