Microsoft invented the MobileOptimized META tag to control the layout width for mobile markup rendered in Internet Explorer Mobile.
http://msdn.microsoft.com/en-us/library/bb159711.aspx
Mobile
Get access to data on 3,320,214 websites that are Mobile Optimized Customers. We know of 1,406,552 live websites using Mobile Optimized and an additional 1,913,662 sites that used Mobile Optimized historically and 781,870 websites in the United States.
Get a list of 3,320,214 websites using Mobile Optimized which includes location information, hosting data, contact details, 1,406,552 currently live websites and an additional 810,026 domains that redirect to sites in this list. 1,913,662 sites that used this technology previously and 781,870 websites in the United States currently using Mobile Optimized.