At PDC this year Microsoft revealed an early look at IE9, what it's targeting, and what the plans are to come. The theory is that IE9 will ship sometime next year, possibly corresponding with Windows 7 SP1.
Here are a couple of links about it first.
Basically Microsoft is going to concentrate on web standards, javascript engine speed, and most interesting, rendering using the computers GPU instead of CPU to speed up rendering.
I'm glad they're finally going to concentrate on web standards as well. Please don't give me the "but HTML5 and CSS3 aren't finished standards and Microsoft will support them when they're ratified" argument. The other major browsers out there support these, get 100% on the ACID 3 test (well, Firefox actually only gets 93/100, still a far sight above the 33/100 that IE8 gets), and when people are writing web apps and cool tech with these standards in mind, IE users get left out in the cold, which isn't good for anyone.
Here's my main complaint with IE. Other than the security issue's it's had in the past, the UI is too slow. Not the rendering speed mind you, the UI. IE's rendering speed is, within reason, completely irrelevant. A 10th of a second difference in rendering msn.com (ugh, what a horrible page by the way), or apple.com or whatever, hell, a 5 second difference really doesn't matter all that much. But when it takes me the count of five to open a new tab in the last updated version of IE on my dual core Windows 7 system, compared to almost instantly in Chrome or Firefox, that's where the failure is. I wish I knew what it was, it's not that silly "automatically detect proxy settings" setting, but it's consistant across the different computers I use.
I think that if Microsoft has the resources to do magic stuff like rendering webpages in the Graphics Processing Unit of my computer, they sure as hell should be able to make the "new tab" function happen in a second or less.
I think that even the IE apologists will acknowledge that some of the UI in IE is sub-optimal compared to other browsers out there. Even if the rendering engines and security were apples-to-apples the same, the responsiveness of Google Chrome and Firefox win out.