Tells owners of the website how many people are visiting the site, where they are coming from and whats most interesting to them.
http://wordpress.com/features/stats/
Analytics and Tracking · Audience Measurement · Visitor Count Tracking
Get access to data on 1,057,351 websites that are WordPress Stats Customers. We know of 48,251 live websites using WordPress Stats and an additional 1,009,100 sites that used WordPress Stats historically and 31,497 websites in the United States.
Get a list of 1,057,351 websites using WordPress Stats which includes location information, hosting data, contact details, 48,251 currently live websites and an additional 101,457 domains that redirect to sites in this list. 1,009,100 sites that used this technology previously and 31,497 websites in the United States currently using WordPress Stats.