I got burned last fall trying to build an app with Ember as they kept making breaking changes, even between release candidates (!). Technically Ember was stable, but Ember Data (which is separate I guess?) was doing major refactoring on their API, and it cost us quite a bit of time just trying to keep up. Even today, their GitHub has a disclaimer that it's beta quality and under active development[1]. Ember CLI also says it's very much WIP[2], even though it seems to be the officially endorsed way to build Ember apps.
Does Angular make stronger promises about their stability? Is this sort of thing just the cost of doing business with cutting-edge frameworks? Or am I missing something?
[1]: https://github.com/emberjs/data#api-stability [2]: http://www.ember-cli.com/#community