As you may recall about a year ago Microsoft announced that standards mode rendering in Internet Explorer 8 would be opt-in only. This caused quite a commotion in the standards movement, and a short while later Microsoft backed off.
Now it seems they’ve backed off backing off, returning to opt-in rendering and taken it a step further by introducing site blacklists. For sites on this blacklist rendering will fall back to IE7 compatibility mode (which isn’t really IE7 compatibility at all), regardless of the actual ability of the page to be displayed properly.
I’ve not yet had a chance to explore this issue in it’s entirety so for now I’ll leave you with a link to the original article on blacklisting in IE8 and how it’s bad for everyone.