This issue occurs because of a design change to how Internet Explorer 9 renders text. By default, Internet Explorer 9 uses sub-pixel positioned ClearType to render text by using DirectWrite, whereas Internet Explorer 8 uses whole-pixel positioned ClearType to render text by using the Microsoft Windows graphics device interface (GDI). [Quoted from the "Cause" section.]

I run a big monitor myself (a Dell 2707 WFP display) and I usually jack up the Web page display to 125% to minimize strain on my aging eyes, so I only noticed this when running my screen at true 100% resolution. But indeed the fix does make formerly fuzzy text appear more sharp and clear. This is one case where a small change in the code apparently makes a pretty big difference in readability on some displays. If your users complain about type that’s fuzzier in IE9 than it was in IE8, this fix could be worth rushing through testing and into deployment.

It worked for me, anyway. Give it a try on a test machine and see if it works for you.