IE7 is finally picking off IE6’s bugs and shortcomings one at a time.
Unfortunately, it has been said that IE7 will not address one issue that is much more relevant now than 5 years ago when IE6 was released: the application/xml+html mime type. I agree that IE7 usage will always be limited by the windows versions/patch levels it is allowed to run on (I don’t see much more than 30% after 5 years).
The only real way to force developers to write compliant markup is for browser vendors to abandon quirks mode completely, or at the very least prompt the user to accept invalid documents before entering quirks mode. Fault tolerance in browsers is out of control.