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 185,302 websites that are Google Content Experiments Customers. We know of 17,705 live websites using Google Content Experiments and an additional 167,597 sites that used Google Content Experiments historically and 6,094 websites in the United States.
Get a list of 185,302 websites using Google Content Experiments which includes location information, hosting data, contact details, 17,705 currently live websites and an additional 40,562 domains that redirect to sites in this list. 167,597 sites that used this technology previously and 6,094 websites in the United States currently using Google Content Experiments.