We use Ember + Rails at work and if we didn't start with an Ember expert contractor we'd have been sunk. Ember is definitely a winding maze of stuff and until there's a "Agile Web Development with Ember 1.0" book, it's still very difficult to just jump in from scratch.
Still, once we've learned Ember we're very happy with it. Backbone is just too small to start any medium/large app, and Ember has a decent community behind it and lots of integrations with Rails.