I've been using Ember Data in all of my applications so far, two of them are in production, another one will be very soon.
Yes there are some rough corners and the documentation is really not that great, but that's something you have to expect from a pre 1.0 release, especially in the case of Data where it's clearly stated that it's unfinished.
The "problem" with Ember is that it's nothing like Backbone, and Ember Data is nothing like $.ajax. It is no surprise that Ember makes you do things a certain way, which is different than most people are used to.
This sometimes leads to thinking that "Ember is broken", but in reality most of the times you're just doing it wrong. I'm not saying that everything is rainbows and unicorns. I'm not even saying that Ember is easy, there's a pretty steep learning curve.
What I'm saying is that once you get past a certain point, most of the issues will just disappear, because you'll know why things "appear to be wrong" and how to fix them :)
I really don't think there's any good alternative to Ember right now, and if you're not satisfied with Ember Data, go ahead and use $.ajax. Discourse does it and it works great for them.