Ballmer didn't get specific when he said the Windows Phone Mango update would bring 500 new features, but we'd bet our blue screens that a handful of those additions are wrapped up in IE9. In addition to the long awaited landscape mode address bar, IE9 for Windows Phone promises to bolster performance through GPU acceleration and an improved rendering experience. The browser update boasts a litany of support features: the aforementioned GPU-accelerated browsing, full-screen video through HTML5 (though not embedded, sorry!), GPS-based geolocation, ECMAScript 5, 2D CSS3, etc. We should know a whole heap of a lot more come tomorrow morning, so be sure to follow along during our liveblog right here.