When Lifehacker asks if its readers would switch to Internet Explorer 9 saying IE9 "looks truly different" you know something big is happening. They have a pretty good overview of the new features in IE9 with some extra exposition on the approach it takes to webapps.
I’m most excited about the GPU acceleration for websites. For more than a decade now I’ve had a GPU that has enhanced my gaming. It’s only been about half that time that the operating system began to leverage the computational capabilities of the GPU. Lately the user experience on the computer has shifted over to the browser and even now most are limited to using the CPU even on high end computers. Adobe Flash 10.1 recently introduced GPU acceleration to its Flash content (at least in a beta release… it seems it actually hasn’t been implemented yet on OS X but I’m quite certain it’s implemented in Windows versions of Flash) and it’s made things much smoother for videos on my laptop. The advantage of GPU acceleration is really for netbook type computers where they can’t have monstrous CPUs to save on battery but when they encounter a tough-to-render page they can get help from the GPU. This combination means even netbooks can have the ability to load high quality websites without sacrificing the battery life for when all that isn’t necessary (such as typing up a document or looking at a simple webpage).