I was quite pleased when I discovered that by accident. I've wanted that ever since win95
Way back when I was using Win 98SE, I installed a utility called Button Boogie from PCMag.com which allowed the user to rearrange taskbar buttons by dragging with the mouse. But, PCMag.com did not create a version of that utility that would work with later versions of Windows when Win 2K was released and then later when Win XP was released. I see they finally released
Button Boogie 2 on September 21, 2007 and it works with Wndows 2000, XP, & Vista.
Like you, I'm glad to see Microsoft has finally added the feature to the OS.