My slightly left of center thoughts on
marketing, business and life in general.
The upgrade from IE6 to IE7 patches about 1000 security holes that would have been too hard to fix without making significant changes to the way IE worked - so that's what they did.
The upgrade from IE7 to IE8 implements as much of the current CSS standards as Microsoft was able to do without changing the way the rendering engine works (because changing trident too much would break windows).
The upgrade from IE8 to IE9 looks like being one where the rendering engine will be changed from Trident to either Webkit or Gazelle. If this is actually what happens then IE will no longer be locked into Windows and will be as capable as any other web browser.
The only mistake that Microsoft made in all this was that they didn't bother with any upgrades during the six years where IE6 had over 95% of the browser market and so fell behind all those that started up during that time. Basically they skipped two releases and so have to do something fast so as to catch up while they still have a userbase left.