I've been using knockout.js for a few months, and find it a daily joy to use. The gains from not having to manage state on the dom or apply your own custom bindings is incredible, and I don't mind not having out of the box model features. But every time I read an over-view of knockout.js vs other frameworks the consensus seems to be that it's great, it results in less code and complexity overall, but it's better suited for smaller projects. This statement is always given as a matter of fact, without much explanation so I'm confused as to what the consensus seems to be. (In fairness I have not used Backbone yet and so don't truly know how they compare)

I've used it on two quite large projects, each with about a dozen models and a dozen view-models or so, and have not seen a problem with it. The only downside I can see vs Backbone in a large project is that you are going to get some non-negligible performance hit for having knockout apply and manage all of the bindings. But is that the main concern or is there something else I'm missing?