What we need in ASP.NET is a change-tracking control. Whenever we modify elements on a form, it would be a good idea to display a popup for user confirmation before navigating away from the page. Right now, I've got some pretty ugly Javascript doing this.
The next version of the AJAX Control Toolkit would really kick a** if it had this control. It could also include bug fixes for the 'focus' issue with the RoundedControlExtender and TextBoxWatermarkExtender.