Free, insanely valuable stuff should be exploited. Google’s Website Optimizer is just such a thing. Essentially, Website Optimizer enables you to figure out what works and what doesn’t on your site.
For example, using Website Optimizer you can easily launch multiple versions of your Call to Action and see hard statistics about which one’s most effective in converting visitors to action.
Visit the Google link above or check out this 37Signals post for examples of how Website Optimizer works.