I grabbed IE9 beta to compare it to FF4 beta for the most part. It is a step up from IE8 that's for sure, and I really like what they did with the UI. That being said it still pales in speed vs Chrome, and is much slower than Firefox when it comes to hardware acceleration. Beyond all those points, IE9 isn't cross platform, which is one of the most important things for me since I can sync up my work PC and Mac with Firefox without having to do anything and can go back and forth with them easily.