Microdata for adding products to Google Shopping.
http://support.google.com/merchants/answer/6069143?hl=en-AU
Widgets · eCommerce
Get access to data on 3,900,785 websites that are Microdata for Google Shopping Customers. We know of 1,036,899 live websites using Microdata for Google Shopping and an additional 2,863,886 sites that used Microdata for Google Shopping historically and 479,018 websites in the United States.
Get a list of 3,900,785 websites using Microdata for Google Shopping which includes location information, hosting data, contact details, 1,036,899 currently live websites and an additional 601,286 domains that redirect to sites in this list. 2,863,886 sites that used this technology previously and 479,018 websites in the United States currently using Microdata for Google Shopping.