Google Website Optimizer will give you a plus minus rate for your estimated conversion rate, which helps you to at least estimate what the significance/confiden

Google Website Optimizer will give you a plus minus rate for your estimated conversion rate, which helps you to at least estimate what the significance/confidence is. For example, one of the pages in one of my current tests shows up as "Est. Conversion Rate: 17.0% +/- 1.4%".