Content Experiments helps you optimize for goals you have already defined in your Google Analytics account, and can help you decide which page designs, layouts and content are most effective.
http://support.google.com/analytics/bin/answer.py?hl=en&topic=1745207&answer=1745147#utm_source=blog&utm_medium=gwoblog&utm_content=content&utm_campaign=content_experiments_launch
Analytics and Tracking · A/B Testing
Get access to data on 179,698 websites that are Google Content Experiments Customers. We know of 17,268 live websites using Google Content Experiments and an additional 162,430 sites that used Google Content Experiments historically and 6,157 websites in the United States.
Get a list of 179,698 websites using Google Content Experiments which includes location information, hosting data, contact details, 17,268 currently live websites and an additional 45,566 domains that redirect to sites in this list. 162,430 sites that used this technology previously and 6,157 websites in the United States currently using Google Content Experiments.