I think the problem with heroku is not scaling but the cost. They use AWS behind the scenes so you are paying a premium over AWS. Eventually that will become expensive. But if you are saving money on labor it's worth it.
Yeah we definitely are. Labor and just plain hassle. It's great to be able to deploy in seconds, rollback easily. Of course its possible to set that up on AWS too - just in practice its always far more complicated than it seems.
The billing is very easy to understand, which is nice. Ive seen AWS billing spiral out of control, yet to experience that on Heroku (touch wood).