The IE Blog notes a very important change in IE7: support of a native XMLHTTPRequest object.
This is good news for developers and site owners as it means that AJAX-style applications no longer need to use ActiveX objects for their IE visitors. ActiveX objects are often avoided when developing web applications for a variety of reasons, so this brings good consistency to the industry.
The other good news is that we're going to see many more AJAX apps in the future, creating all sorts of analytics challenges and opportunities.
Oh, and yes, Firefox supports the XMLHTTPRequest object too.