keithpitt/ember-rails — pull request #3 by dgeb (2012-01-13 19:06:45+00:00)
Title: Include support for .handlebars extension

Apparently, @wycats (the creator of Handlebars) prefers the .handlebars file extension:

https://twitter.com/#!/dgeb/status/157591512136433664

I've also seen .hbs used, but I'm not sure if you want to support all three.