In practice, the biggest loss-of-control problem I have with Heroku is that it dictates my choice of programming language. Of course, choosing a Linux server also dictates some choices, like making it hard to run Windows-only software. But for me at least, the Linux-apps-only restriction feels less constraining than the Heroku-approved-languages-only restriction. I tend to experiment with new languages semi-frequently, and also have a bunch of code in languages that Heroku doesn't support (mainly Lisp).