It seems like all the preferences are geared towards landing/info page sites.
What about full on Facebook / Gmail / Forums / CRM type web-apps?
How they have front-end user experiences and full on admin specific user experiences that are completely different. With all kinds of users in different companies, where there are all kinds of views depending on the action of the current user. Adding/removing features based on users or group memberships etc
I like the Ember.js framework ideology. My biggest annoyance with these frontend frameworks is the all or nothing part. If someone loads up the signup page, they don't need the admin app or the full logged in user part yet, even if they are logged in, there needs to be a balance between first response and quick 2nd page. Ember has engines finally to help with this.
On a page by page basis I like the simplicity of other frameworks/libraries, however to get some efficiency across the whole app, spending time making components inside a full framework and stitching them together in the page as needed has been great. For example with a simple information game (think rpg, clan, army kinds), while the REST way was fine every single resource on its own page works it was super slow to get anything done. I needed lots of information from many endpoints on the page in their own little space on the screen and they all needed to update based on actions happening in the backend.
This is where I see a full framework like Ember.js being a great fit. If I were building a landing page/informational product site I'd go pure HTML with a helper if needed to make something appear instantly responsive to actions.