Today at MIX10, Microsoft unveiled the next generation of Internet Explorer browser, IE9. IE9 uses a new JavaScript engine called "Chakra" which has boosted it’s performance as compared to IE8 and browsers like Opera 10.10 and Firefox 3.6, putting it behind Safari, Google Chrome and Opera 10.5.
IE9 also supports HTML5 and CSS3, however, it falls way to shot in Acid3 tests scoring only 55/100 which is worse than most of the other browsers. IE9 supports GPU or hardware accelerated HTML5, which means that graphics and HTML5 videos will play much better on IE9 because it will utilize the graphics card for better performance.
The IE blog has a much more detailed post on the new features in IE9. If you are interested, you can download a preview version of IE9 from here.