Not sure if you've heard already, but Google Optimizer is now out of beta (it was previously only available to people who had an Adwords account). The service lets you do A/B testing, to see which site design/ad blocks/link positions convert to more sales and a lower bounce rate. Sounds like a good tool for those who are about to release a new site, or at least a new site design.
Without hunting through their documentation for the answer, is this thing designed for webmasters that use Adwords and/or Adsense, and to hell with the rest of us?