, intelman wrote

What is up with DirectWrite? How come it looks fine on some pages and horrible on others? To me this is the most significant change of the web. Text readability on digital displays will only become more important.

Firefox 4 also seems to have adopted this notion that we should be using directwrite.

This blog entry by the IE team might share some light on that: Nov 3, 2010: Sub-pixel Fonts in IE9.