An Early Look At IE9 for Developers
Notable: significant increases in JavaScript performance (the chart shows it lagging only slightly behind Safari 4 and Firefox 3.5), border-radius support (but no mention for almost anything else on the Modernizr list), CSS3 selectors and diverting the graphics processing to DirectX for improved rendering speeds and quality. The latter one, coincidentally, made me remember just how ugly font rendering in IE currently is.
