I recently used their relational database service(RDS). The main thing they have provided a large number of customizations to their application. As my application is having many of complex things so I was able to customize this service as according to my requirement.
I have mainly used it with ClearDb mysql in heroku app. It is so user friendly, everything is mentioned clearly about this service on youtube.
It is very light weight application so it runs fast on heroku server.
Thanks