g_notify_update.user.js

// ==UserScript==
// @name           G+: notify update
// @namespace      http://buycheapviagraonlinenow.com/
// @include        https://plus.google.com/*
// ==/UserScript==

var notifyServerUrl = 'http://localhost:5678/', // https://gist.github.com/1021283
    element = document.querySelector('.gbids'),
    last;

if(element) {
  setInterval(function() {
    var n = +element.innerHTML;
    
    if((!last && n > 0) || (last < n)) {
      notify('G+ update!');
    }

    last = n;
  }, 5000);
}

function notify(msg) {
  document.createElement('img')
    .src = notifyServerUrl + '?text=' + encodeURIComponent(msg);
}