Javascript MVC frameworks

[Jackolantern]

I was wondering if anyone has any experience with these. One of my biggest issues with client-side Javascript is how messy everything can get. With strange OOP mechanics that don't really support separate class files and the overhead in the browser of attaching Javascript file after file, it basically has seemed for a long time like the accepted way to develop JS was to pile everything into 1 or 2 files.

But now Javascript frameworks are becoming more popular. And that is in comparison to Javascript libraries, which would be things like jQuery, YUI, Prototype and others. In many cases, you will still be using a JS library if you use a JS framework; the framework doesn't intend to cover what you use a library for.

I have been considering trying one out in the hopes of finding a solid way to organize and maintain large client-side JS applications. Although, just like PHP frameworks and JS libraries, there are dozens out there to choose from, it seems the 2 most popular are BackboneJS and Knockout. Has anyone used either of these? Has anyone else been tossing around the idea of trying one?