A few days ago I upgraded to Microsoft Explorer 8. Was hesitant first, as new versions often have problems. But I must note that I was pleasantly surprised - no problem so far. One add-on was automatically disabled, something to do with a DriveLetterAccess (not sure why I need that in the first place...).
Some friends of mine had trouble: a lot of DEP exceptions in the add-ons, flash or images would not show up. But miraculously, these problems disappeared after a while, without any specific measures.
One issue is there, however, with the Blogger site: when logged in, the blog posts now do not show the edit-shortcut link below the post. This works ok in Google Chrome, and it used to work ok in IE 7 and earlier.
One other thing I noticed: the Microsoft Photosynths work now in several browsers: Google Chrome, Firefox, MS Explorer. I will add soon a few more there.