CSS3 box-shadow
Chris Casciano: CSS properties box-shadow and rgba() and others like text-shadow are absolutely usable in the wild right now.
Works fine on elements that are position: fixed (example: my nav bar). When I try to put it on either my articles or my section h2s, scrolling becomes jerky on Firefox 3.5.3, but remains smooth on Chrome 4.0.222.5. Primary environment is Ubuntu 9.04, but I see similar things on Windows XP.