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.
We're working on https://github.com/rails-api to make Rails a great backend for APIs, and specifically Ember. Team is mostly Rails Core members and Ember team members.
The hope is to make it awesome for other JS frameworks too, but we mostly build Ember apps ourself, so you start with what you know...
Glad to hear rabl is working well in conjunction with rails-api. Haven't had a chance to try that combination yet, mostly been using rabl alongside Sinatra, Grape and Padrino.
Totally. And there's a reason AMS isn't part of rails-api proper: we want you to pick the tools you want to use. If rails-api (the gem) doesn't work with RABL in some way, please let me know, that's a bug.
You haven't seen the full power of AMS yet, but I have some exciting things planned. :)
You can do both, for example, you can use rails for authentication with traditional views and then use ember for the main single page app. I think this is how square does it.
Also you should look into active model serializers for integrating rails with ember. I think it's yehuda Katz' preferred method for Jason serialization from rails to ember.
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.