I'm aware that you might be asking in a more application-developement oriented sense, but I'm a web designer, and here are my experiences-
I spent a day each in both GoLive and Expression Web, but after using both to try to create a CSS-based standards-compliant site, I quickly switched back to notepad.
One thing that I noticed, with Expression Web, was that the edit mode and IE7 rendered the page *very* differently, in relation to the CSS styling (mostly concerning the box model and alignments). These are familiar problems to any web designer, but it's still
unacceptable for a WYSIWYG editor to display differently than it's default "preview" browser.