Having installed the Internet Explorer 9 release, I've experimented with the jumplists feature available in Windows 7 - drag a site tab down to the taskbar to create a jumplist. Works for Facebook and Twitter, anyway.
I have my suspicions about the utility of this feature - it's a neat and possibly useful feature, yet is limited to the combination of IE9 and Windows 7, plus sites implementing the appropriate code.
Given the relatively small audience at this point, is there any value in adding code to support this feature? And would it likely be more useful for a web application (e.g. Twitter, Facebook) than a typical website?