I've been messing around with Play, and decided that I'd push it up to Heroku based on the tutorial and things I've heard about Heroku.
I'm going to expand on this later but, if you forget the Procfile when deploying your Play application, it may cause your app to get totally jammed and never be able to start. I spent the next hour or two trying to figure out why my app wouldn't start, even after I'd put the Procfile in.
I solved the problem by deleting my app on Heroku and creating a new one. Then it started fine.
The docs on pushing a Play 2.0 app to Heroku all disagree with one another too, so I hope I can find a few to post a tutorial based on how I got it working!