Many of the largest sites on the internet don't use them in any significant way, and you could just as easily use Django to server HTML/CSS to browsers, as well as a Rest endpoint for mobile apps or other users of your data.
I have used a fair number of websites recently which used front end frameworks badly and ended up causing all sorts of havoc (not being able to save the page, random {{ things like this }} appearing all {{ over }} the place at inconvenient times, pages just not loading, janky controls, etc.)
In short, bugs that don't happen when you have static web pages and forms and a smatter of javascript.
In almost all of these cases I think users would likely not have noticed a substantive difference between an angular-style web app and simple HTML forms.
I'm a huge fan of Backbone. Its small enough to learn the in's and outs of it and also allows you to control the structure / design of the application.
This definitely has pro's and con's but for us it means we can swap developers and theres a design pattern thats easy to understand and implement.
We're actually building a pretty large Ember project at the moment (a project management tool called Matterhorn). Its been a great experience and we're planning on using it for all of our client projects going forward.
The learning curve is a little high and the 'plugin' eco-system is lacking to say the least. I actually think this is a good thing though as most people write terrible plugins. Roll your own and own it.
He came to that decision just after we committed to angular... :(
Having a glance at Mercury. Looks interesting, but react is working so well for my projects I'd need a damn good reason to give it up.
To save the next guy some googling:
Now I'm trying to figure out if the bad parts in Angular are worst than the bad parts in React. I don't have an answer yet.
The only thing I'm sure is that the virtual-DOM thing is a good idea and most frameworks are likely to converge here.
Which are...?
My current app is actually still back on Marionette 1.0.4 for various reasons, so I'm not as familiar with the changes in the latest versions of Marionette. Looks like they've added a considerable amount since then.