I've worked on large javascript applications written in Ember, Angular, JavsacriptMVC (now can.js), and jQuery and the conclusion I've come to is that things have not settled down in the world of front-end development enough to justify a framework as opinionated as Ember. For example, Ember relies very much on routing being handled a certain way. In fact, much of the magic in Ember comes from the fact that it's making a lot of assumptions about how routes are handled, constructed, and organized. This is great if you can assume that an app's routes will be written in a very traditional way, aka one route per page. It breaks down however when you want to tie different routes to two or more components on the same page (i.e. two different tabbed sections). One concern per route makes perfect sense on the server when serving a traditional stateful web application but it often doesn't make sense for rich desktop-style applications (which is probably why Photoshop doesn't have urls).

Data persistence on the client is another area I feel hasn't been nailed down in general and thus can't support a lot of opinionated assumptions. Should data be persisted at all? Ember caches data from all requests to the server in a "store", but it's not clear how you keep that cache up-to-date. Perhaps you could use websockets to keep resources current but at the time I was using Ember there wasn't a clear, well supported way to do that. I think the jury is still out on whether we should be duplicating our schema on the front-end at all but Ember-Data has gone all-in on mimicking ActiveRecord. Again, the dust has not settled in a lot of areas of the front-end development world as far as I'm concerned so I don't feel comfortable with these decisions being made for me.

I tend to lean toward convention over configuration. On the server I'm a big Rails fan but I feel like it's solving problems that aren't moving targets. On the front end I prefer Angular because it solves the main headaches (two-way binding, testability, modularity) of front-end development without being too opinionated about the stuff we haven't reached consensus on.