So Microsoft, which is more known for its PR than its performance, claims Javascript is a moot point. Yet Google, Mozilla, Opera and Safari are all working to improve their performance with JS...
So far, until just recently, all we have seen of IE are 'previews' based on their own set of demos. Its kind of like Google saying they have the best performance on the V8 benchmark when they tuned the engine around the benchmark... Incidentally, Firefox is the only one of the 4 other browsers that can perform decently on those demos. It's always suspicious when Microsoft makes claims about performance, especially when its using its own tests.
Another issue is Microsoft has NO plans for IE9 for XP. They did it before with IE7 for 2000. They'll probably do it again for the next greatest OS. Most companies don't go upgrading the entire organization's PCs to the latest OS every 3 years. These days, they are sticking with OS longer. Microsoft focus long ago stopped being about the consumer and about businesses. Every time they tried to kill off 2000 and XP, businesses have cried foul and MS has backed up from their plans. (Consider if you have just 100 computers, and it costs $50 (in a dream world) to upgrade each PC. That's $5000. 1000 computers, that's $50,000. For $50,000 you could buy 100 new entry-level PCs which last you another 3 years vs upgrading the OS which the return on investment is questionable).
Firefox and Opera still support Windows 2000. Supposedly you could run Opera on older Windows. Safari and Chrome will likely continue to support XP for some time (isn't it funny that APPLE supports XP which is NOT their platform but MS doesn't?).
Incidentally, if you install IE9, you loose your stable, patched (for what it is worth) browser for an unproven, unstable browser. Microsoft doesn't bother to ask you. Microsoft doesn't even bother to TELL you. I say that's pretty insincere of Microsoft saying they are focused on what their audience needs. There's also a whole list of things that can go wrong per Microsoft. IE9 seemingly would not install on my system. It threw an HTML file on my desktop documenting all the different issues that could occur in installation.) I rebooted and tried to install again at which point it told me that a NEWER version of Internet Explorer was installed.
Each party behind each of the browsers have their opinion of what the experience should be. Personally I like Firefox. When Netscape died off I took up Firefox and have kept following it. However, I believe each camp has their valid points and they will appeal to different people. Some people even use more than one browser for different reasons.
As for benchmarks, it is at the very least a starting point to compare the browsers performance-wise beyond 'Oh, I think Chrome just runs faster than Firefox.' When Kraken (Mozilla's benchmark) came out, Beta 6 actually scored below the other browsers. But even with certain prejudices assumed, you start to see patterns across all the benchmarks. Webkit (the underlying engine for Safari), Google, and now Mozilla too have JS benchmarks. Servicemark (makers of 3DMark) created a rather nice (and free) benchmark entitled rather interestingly 'Peacekeeper.'
So we have four different camps (one of which isn't even involved with Browsers) involving similar tests (although Peacekeeper also tests Canvas, which is a new non-plugin graphics rendering element in HTML5).
I think we all should continue to take what Microsoft says with perhaps a whole shaker full of salt especially when what they are saying flies contrary to what everybody else is doing.