Amazing. Way back in 2007 I taught myself how to code by making small Facebook apps. I started out by editing live PHP files on a shared server from A Small Orange ($3.33 a month!). After a few months I a few apps with traffic around 30k DAU. A Small Orange would automatically shutdown the apps every couple hours. I'd email them and complain about their shoddy hosting service. They'd always respond instantly apologizing and putting the apps back online. After a couple weeks I realized that I had a scaling problem and began learning how to setup a dedicated server. Over the next two years I spent about 80% of my time wrestling with hardware, setting up load balancers, configuring cache and db servers, and other operational nightmares. I had little time or energy to work on improving my apps or building new products.
Then I discovered Heroku. I would have done anything to have this when I started out. The platform teaches (forces) you how to build a scalable architecture. You can try out new ideas for apps for essentially nothing (1 dyno is zero dollars). Since moving to Heroku I spend about 5% of my time working ops. The craziest thing is I've actually saved money since switching from dedicated hardware to Heroku. I was really bad at configuring servers and the stuff I built was inefficient and expensive. Heroku's cloud stacks are optimized better than my old hardware environment.
Heroku's architecture is great for wild traffic swings common with Facebook apps. Well except for their database services. They don't seem reliable or scalable. I prefer RDS.
In sum, Facebook and Heroku is a great starting place for learning to build web apps. I would have done anything to have this tech four yeas ago.