Yep, we really should have someone fill in http://trac.qcu.be/projects/qcubed/wiki/changelog with details on 2.0 soon.

In short though, 2.0 is primarily a re-write of all the js in the framework to utilize jQuery (in compatibility mode, so you can still use other frameworks with QCubed such as Mootools). This should result in more streamlined js, better browser compatibility, fewer js related bugs, and easier integration of nice client-side functionality.

And if we're lucky, it will also mean better js performance, but I wouldn't expect any noticeable differences in that department.