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genem, here's some info for you - quoted from the AdWords Help Center:
Website Optimizer is designed to keep your original content visible in the HTML source code of your page at all times. As a result, your original content is visible to crawlers, which means there should be no major impact on search engine ranking. However, if you implement changes to your content after using Website Optimizer, they'll have the same effects as any content changes that you would typically make to your website.