Only problem with GWO as compared to Visual Website Optimizer or Optimizely is that you have to create a separate version of the page you're testing yourself. GWO then redirects to visitor that alternate page--so Google warns:

"These URLs could be bookmarked by your users, so after your experiment finishes, you may want to keep these URLs valid."

I'm not if I want to have a bunch of redirects set up after I finish the experiments to make sure no one gets a 404.