while this is an interesting reply, it could be way more interesting if it contained a "because ...." subsentence, could you expand on this?

We build online trading applications with KO (we use it only for the view, we have our own Presentation Model were we have observers which pretend to be KO observables) and we have found it quite helpful.

The components built are FX tiles, trade and order tickets.

what do you mean by non-trivial?

I've abused knockout to some rather interesting ends, but I've never attempted to use it for as an in browser MVC setup.

I think of Knockout and Backbone as fulfilling two different purposes.

As opposed to Backbone, which doesn't bite you hard?

Dude Backbone only works for trivial examples, and even then, and I mean, even with trivial examples, Backbone is almost useless.

I haven't yet been bitten by Knockout in any bad way.