Microsoft originally announced they weren't going to release a new version of IE until the release of Vista. They changed their minds, obviously. In light of mounting critism on multiple fronts, security, web standards, the rising popularity of Firefox, I'd say they made the right decision. The announcement that there would be an IE7 before Vista wasn't made until maybe a month or so after Beginning CSS hit the shelves, and at that, the final product might not come until Vista's release, which is expected some time this year.
I've only been able to look at IE7 breifly, it has its own bugs naturally, but my first reaction is there have been loads of fixes, and while it's not perfect, it's an improvement by leaps and bounds. I looked at some of the examples from Beginning CSS in it, and alot of the examples I tested appear either as intended or close. Looking at the WASP Acid 2 test for standards compliance in IE6 beside the rendering in IE7, shows that alot has changed. Even though it doesn't pass the test, it's much closer to that goal than IE6 ever was.
Hope that answers your question.
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