SuperSite for Windows posted a preview on Internet Explorer 9. Here's a bit:

With IE 8, Microsoft argued that browser performance wasn't something that could be easily measured with benchmarks because overall performance is more holistic. The company's success at communicating that message is debatable, and while Microsoft's own published performance results were pretty favorable, IE 8 tends to get pummeled in independent comparisons with Mozilla Firefox and Google Chrome.

For IE 9, Microsoft appears to be addressing IE performance issues head-on. The company explained this week that it examined how similar sites actually tax browsers in different ways--some are script-heavy, for example, while others are not--and its architecting IE 9 to handle these different needs properly.
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Working hand-in-hand with Microsoft's performance aspirations for IE 9 is a surprising browser capability: GPU-backed hardware acceleration. "This is the coolest but least understood aspect of IE 9 we announced," Hachamovitch said. "We've moved the IE rendering engine from GDI to DirectX."

There are two benefits to this approach. First, the web doesn't have to be rewritten to take advantage of this functionality, as it's just provided by using IE 9. And second, web developers can now seamlessly take advantage of all of the benefits associated with PC hardware advancements that have happened over the past few years. The GPU is no longer just used for games, 3D user interfaces, and other graphics-intensive applications.