Scott Hanselman discovered that Outlook is using proprietray feed URI schemes under-the-hood; OUTLOOKFEED: and OUTLOOKFEEDS:. As if the feed: URI scheme wasn't already dumb enough, now Microsoft is going and breaking the architecture of the Web again. Let's just hope that this is an internal thing that'll never find its way onto the WWW.
http://www.hanselman.com/blog/Outlook2007BetaIntroducesItsOwnFeedURLProtocolEw.aspx
Thanks to Marjolein Hoekstra for the link [play tag with me].