@battlebottle: Thanks for the info. That explains why in VS 2010 beta the font looked bad and appeared to be fixed in RTM.
I have been using IE9 full time since Beta. It is not terrible but I definitely notice the difference. When I sense a difference (negative) in the font, the first thing I look for is a grey border around the page which tells me if the page is rendered in IE9 Standards mode. If it is awful on a particular website, hurts my eye, I just switch to IE8 Standards mode.