For what it's worth, I suspect IE8 is going to stand out much more than IE7, which very few people will upgrade to (IE7 doesn't exist for Win7 I don't believe, so as people upgrade to Win7, you will see surge in IE8).
But nobody (we hope!) is writing IE specific apps anymore right? This is the whole reason IE6 is still around, because 10 years ago people WERE writing to IE. So I would suspect IE8 will have much less inertia.
I suspect it will be more about IE8's lack of support for CSS3 (and HTML5), meaning that we will have to keep bothering with various tricks and libraries to (partially) fix these for us.
