Read Joel on IE8, standards and the mother of all flame-wars.

He thinks it will "break the web".

Update : he's wrong (sort of) about Postel. The point is that Postel wasn't trying to make a reference implementation. There's be nothing to stop the W3 making a reference implementation of the spec. and just telling M$ etc. to conform or be non-standard. That's not Postel's job though. His law is designed to get a flawed communication system off the ground, not to ensure standards. (As Spolsky kind of admits)