The open source engines are rockin' the speed game and the closed engines are falling very far behind very quickly. It looks to me like the closed and proprietary guys just can't keep up.
Photo "No longer rocking" by Gary Simmons used under a Creative Commons license.
It's actually a shame that they're falling so far behind. It would be helpful for the Web if the IE team was able to make some serious JS improvements for 8 and whatever comes next because there are still a significant number of users stuck on Microsoft's technology.
Their falling behind won't completely stop the Web from moving forward though. There's enough momentum behind the truly modern browsers, Firefox leading the way with 20% of the market, that the Web will get better without them.
IE market share will continue to deteriorate, probably at a somewhat faster rate, as users flee for a better experience. And MS will no doubt slow things down at least some so I really do hope they improve. The less of a drag they are the better.