My concerns are that Heroku's prices are rather high. I understand paying for what you use, but you get charged for as long as something is on, even if it's not in use. Add to this that there's no built-in shutting down of inactive dynos or workers, and you can't help but feel like you're getting fleeced.

I haven't looked at Rackspace too much. Is deployment as simple as a git push, like Heroku? How's their pricing compared to Heroku? Is rolling your own scalable Rails architecture using AWS directly too complicated?