In fact we started the project in june 2013 because even though we were very fond of the way of thinking proposed by Heroku (git push and that's all), their pricing was way too high to target a lot more people.
Since 6 months, I've got a couple application in production there. Got a couple bugs during the beta, which were quickly fixed apart from that everything is fine.
I am using them for many months, works great for most of my projects, easy to maintain, easy to scale.
Love that they support Meteor natively, without a specific buildpack to install.