jQuery 1.6 will feature much improved performance of jQuery's attr() and val() methods. For the first time, the library will include support for boolean attributes and hooks. Event handling performance has also been greatly improved, which will boost performance of jQuery's data() function.
On the cross-browser compatibility front, jQuery also features a number of improvements. The ":focus" selector works properly across a wider array of browsers. The find(), closest() and is() methods now all take DOM elements or jQuery objects. The update will also bring developers smoother, better synchronized animation.