Timed rotating header image
This script will change the header picture every 15 seconds. Start with the default pebble theme and place the script just before the closing tag to the div with an id of "header" in template.jsp.
<script type="text/javascript">
window.setInterval(function() {
var x = document.getElementById('header').style.backgroundImage='url(themes/user-default/header'+Math.floor(Math.random()*3)+'.jpg)';
},15000);
</script>