So at Microsoft's MIX developer conference today in Las Vegas, Microsoft VP of Windows Phone Program Management Joe Belfiore did a little HTML test showing IE9 on a future version of Windows Phone. And it appears to blow the Nexus S and iPhone 4 out of the water.
What's odd is that I can't even get the Nexus One I have here to run it that well. Want to try it yourself? What sort of magical sorcery has Microsoft unleashed? Dunno. But you can give it a shot at this link if you want.