[_bpo]

You get lockin issues with any vendor - even server colocation :)

AppEngine is a great tool for a great price. It scales smoothly with an affordable increase in pricing.

Heroku is sort of famous for getting too expensive at large scale. Their advantages are their ecosystem (most of the additional services listed in the OP can be installed quickly, and you're still only billed by Heroku), and their UIs which tend to be easy to understand and operate.

[campers]

Parse.com is similar to Heroku in that its simple to get started and has a free tier but gets real expensive once you go over that. I'm rebuilding my Parse back-end and going with Google app engine managed vms for a number of reasons.