Beta 2 of the developer toolbar is now available. Beta 2 includes numerous fixes to improve stability, usability and performance along with a couple of additional features such as the ability to enable and disable CSS on the page. The developer toolbar has become an essential tool for us in diagnosing issues with web pages. Being able to click on an element in the page and find out where it is in the element hierarchy is just one of the invaluable facilities it provides.
Although it's not as user friendly as the one for Firefox, it does allow you to debug web development issues more easily.