If used correctly, no. Currently most web crawlers/bots do not execute javascript. Because GWO uses javascript to redirect visitors and alter a page’s content, a search engine doesn’t actually see the pages you’re testing. Designing a page to present differently to search engines vs human visitors is actually counter to Google’s Webmaster Guidelines. When you get to the end of the test, if you find that one of the variations performs better than the original test, then you will want to continue using it. If you replace the original page with the new page then earlier SEO juice will be lost. However, it’s ok to leave the original page and to continue with GWO post test – Google recognises its own JavaScript code and won’t penalize the site in its rankings.