Microdata for adding products to Google Shopping.
http://support.google.com/merchants/answer/6069143?hl=en-AU
Widgets · eCommerce
Get access to data on 5,527,957 websites that are Microdata for Google Shopping Customers. We know of 2,257,077 live websites using Microdata for Google Shopping and an additional 3,270,880 sites that used Microdata for Google Shopping historically and 1,124,365 websites in the United States.
Get a list of 5,527,957 websites using Microdata for Google Shopping which includes location information, hosting data, contact details, 2,257,077 currently live websites and an additional 1,357,491 domains that redirect to sites in this list. 3,270,880 sites that used this technology previously and 1,124,365 websites in the United States currently using Microdata for Google Shopping.