How KISSmetrics uses the 'identify' API call.

identity_tracking.erb

<!-- KISSmetrics -->
<script type="text/javascript">
var _kmq = _kmq || [];
var _kmk = _kmk || 'foo';
function _kms(u){
  setTimeout(function(){
    var d = document, f = d.getElementsByTagName('script')[0],
    s = d.createElement('script');
    s.type = 'text/javascript'; s.async = true; s.src = u;
    f.parentNode.insertBefore(s, f);
  }, 1);
}

/* Notice the logic here.
 * 'identify' should be included only when the person is currently known.
 * If you're not sure who a person is on a given page, then don't include the API call.
 * Alternatively, this is safe to use if the person is unknown:
 * _kmq.push(['identify', '']);
 */
<% if @current_user and @current_user.current_account.is_a?(Account) %>
  _kmq.push(['identify', <%= @current_user.login %>]);
<% end %>
</script>