It's great that they are trying to improve things over at Microsoft, but I'd like to point out a few things as to why this could cause more pain than joy.
Looking at the stats over at w3schools which gives us a rough indicator of the break down between IE6 and IE7, they both have pretty close market share. Although IE7 is now in front it has taken some time to get there and IE6 is still refusing to die. With the introduction of IE8 we may be looking at three browsers in existence all with a reasonable amount of market share. Enough for those people who you are designing for to ask that there flashy new web site still renders well in all three browsers.
A couple of years back we were developing for IE6, IE7, Opera (and then Safari) and Firefox. We now have Chrome and IE8 now thrown into the mix. The biggest problem is that all these browsers render a page differently. Meaning more work with each new addition.
I don't want to go into detail about why it is good to have standards; it just seems with each release each of the majors does most things right, but it's the little things (except for IE6) that make life so hard.
I read this blog today on zdnet about which "big" sites had not yet prepared for IE8. I thought it was an interesting point of view that it was expected that these sites should be ready for another browser that has not yet been released. The other thing that the article mentions is the new 'Compatability View' button. This will allow (from what I have heard) sites to be rendered according to the way they would in IE6 or 7.
So... it has taken almost two years for half of the IE users to come on board with IE7. Why would they bother going to IE8 when it won't render pages the same unless you click on a button and then it will just be the same as the browser they just gave up.
It seems they still haven't got it right, with IE8 not passing the ACID3 test although according to Microsoft it apparently passes ACID2.
The past couple of years have been quite interesting with XP still refusing to die and IE6 refusing to die. When the guys at Microsoft come out with something that's nice and does great tricks (ala Office 2007) people flock to it. It would be better if they took the same approach with IE and come out with something that is the best in the field and not something that is playing catch-up with a backwards compat. button.
As they keep delaying, let's hope they're listening and come out with something that is worthwhile for the end-user. Otherwise we will continue to see Firefox eat away at their market share. Also we live in hope in one day IE6 will go away.