Last week one of the guy's at our office did a talk on using Google's Website Optimizer for AB multivariate testing. In the talk, he says that when you set it up you just add some special code to the page around the HTML you want to vary [ see #3 under multivariate test here ]
<script>utmx_section("Headline")</script> Welcome! </noscript>
What's going on with that unbalanced tag at the end? What magic is Google doing?