Microsoft claims IE8 will have strong support for HTML5.

On August 31, 2007, lead IE developer, Chris Wilson, posted this:
A while ago, I signed up to review the HTML5 spec by the end of August; unfortunately, that will not be complete today. I now expect to send comments by the end of next week (9/7).

-Chris
To date, Microsoft has not made any such review.

Microsoft is co-chair of the HTML5 working group.