Microdata for adding products to Google Shopping.
http://support.google.com/merchants/answer/6069143?hl=en-AU
Widgets · eCommerce
Get access to data on 4,069,733 websites that are Microdata for Google Shopping Customers. We know of 1,083,803 live websites using Microdata for Google Shopping and an additional 2,985,930 sites that used Microdata for Google Shopping historically and 498,514 websites in the United States.
Get a list of 4,069,733 websites using Microdata for Google Shopping which includes location information, hosting data, contact details, 1,083,803 currently live websites and an additional 662,513 domains that redirect to sites in this list. 2,985,930 sites that used this technology previously and 498,514 websites in the United States currently using Microdata for Google Shopping.