Internet ExplorerBrowser Info Environment
However, the edit interface requires IE7 or greater and the ajax magic will not update the page metadata in versions less than IE8.
This should not be an issue for webmasters, editors and administrators as we are likely to be using up-to-date browsers, or at least browsers that are not too far out of date. As long as the site is generally viewed in such browsers, the ajax part of magic heading will run often enough to keep the metadata up to date. (Just think of IE6 or IE7 users as an additional throttle setting)