[rimantas]

  > It seems like there's too much complexity

Backbone helps you to do the things you understand. Knockout let's you do things you don't necessarily understand. Sometimes black-box approach is OK. Sometimes not.

[hasenj]

Knockout, while it seems magical at first, is actually not so hard to reason about.

It's not really a "blackbox". It's quite easy to understand and extend too.

For instance, you can create your own custom bindings: http://knockoutjs.com/documentation/custom-bindings.html

This is about the only place where it gets low and dirty and involves you writing DOM manipulation code.

[pserwylo]

I'm not familiar with Knockout, but it sounds like my experience when we were getting into the Flex framework at work a couple of years ago. We thought the data binding was so magical, but once I started to work with it, I had a very good mental model of how the MXML/ActionScript compilers were doing their magic.

It was much more pleasurable to work with when it was no longer magical.

[romaniv]

I'm not familiar with either framework, but at least I can understand the intent (if not mechanics) behind Knockout code. With Backbone, it's like reading a whole different language.