I use Expression Web 4; I have uninstalled IE9 beta.
When IE 9 was installed I noticed that some fonts (Trebuchet MS and Arial) were both fuzzy in comparison; Trebuchet MS font also appeared 'thicker/fatter' in IE9. Is this a problem with IE9 or the W3C CSS specifications? Segoe UI font seemed OK. The font Trebuchet MS looked 'normal' when my web site was viewed in compatibility mode, without 'thickening' of the fonts.
There is no mention of a pending update for Expression Web 4 (to keep up with IE9) in the Expression Web forums.