This is certainly a promising development in these times of antitrust complaints and "wars" over standards. Acid2 only tests a smaller portion of certain standards, so it will be interesting to see the first public release of IE8 and how far along it is when it comes to open standards.
In any case, congratulations to the IE team, and I hope this is only a tiny first step in the process of turning IE into a standards compliant browser.
Our Web Opener, David, has written a longer piece with his thoughts on this interesting development. Needless to say, he's a happy camper.