My experience has been pretty good. I like how fast it is, how it enforces immutable deploys and how user friendly the CLI is.
The only thing I stumbled upon is that deploys start to sleep after ~1 hour of inactivity. This is, of course, a great way to save unnecessary applications from running. However, it means that when you 'wake' a deploy up by sending a new request, it can take up to 30 seconds to get a response.
For production sites that's simply unacceptable.
One way to solve this problem is by running a cronjob on a different server that performs an HTTP request every hour, to keep the deploy running. Which isn't really elegant in my opinion.
TL;DR; It's great for quick prototyping, but I wouldn't use it in production.