I downloaded Internet Explorer 7 (Beta 3) today, just to see what the buzz is all about. Comparing it with Opera and Firefox, the only difference I see is that (out of the box) IE uses ‘ClearType’ to render the fonts. The other thing I noticed is that the specific copyrights portions to Spyglass have been removed. 
Maybe they’ll be added after the final release. Maybe not. However, IE 7 (besides the ‘gadgery’ new features) clearly behaves as regular Internet Explorers, which tells me that in fact changes to the renderer aren’t too spectacular. If you install IE 7.0, I’d like to remind you that it will replace your existing Internet Explorer. If you develop on older IE versions, you may want to skip the ‘upgrade’.
That said, when opening the WP dashboard in IE I noticed the ‘BrowseHappy’ button. This button naturally doesn’t appear in other browsers (Opera/FF). A grep confirmed this: the code is in one of the admin-functions php files (see image).
Is this evil? You know: I honestly don’t care.