Once per session tracking

session.js

(function () {
  var traits  = analytics.user.traits()
    , session = traits.session
    , now     = +(new Date); // shim for Date.now in older browsers

  if (!session || (now - session) > 60*60*1000) {

    // Track things which happen once a session
    analytics.track('Once a session');

    // Update the user
    analytics.user.update({ session : now });
  }
})();