I stumbled over this whilst trying to work out what this tag in my WordPress theme meant: <link rel="profile" href="http://gmpg.org/xfn/11"> Does anyone

I stumbled over this whilst trying to work out what this tag in my WordPress theme meant: <link rel="profile" href="http://gmpg.org/xfn/11"> Does anyone actually use FOAF or XFN, and if so why?