In a startling turn of events, Microsoft has reversed an earlier stupid brain-dead decision, and is actually doing the right thing.
Internet Explorer 8 will have much better support for modern web standards than IE7 (which in turn has slightly better support than IE6). Apparently the internal builds already pass ACID2 (IE7 and Firefox 2 do not; Firefox 3 and the current versions of Safari and Opera do). However, the original plan was to only enable this improved standards support if the web developer specifically requested it by adding a special META tag; by default, IE8 was to operate in an IE7 compatibility mode. The goal was to avoid the problem of non-standards-compliant sites breaking when users upgrade their browser, which is what happened when people upgraded from IE6 to IE7, but it would have caused serious problems in the future.
Basically, it was a really bad idea, but Microsoft has changed their minds. They're doing the right thing, because it's the right thing to do. The last time I remember Microsoft going out of its way to do the right thing with IE was when they met with the Mozilla team in November 2005 to discuss using the same icon for RSS feeds in IE7 and Firefox.