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 4,030,418 websites that are Mobile Optimized Customers. We know of 1,660,325 live websites using Mobile Optimized and an additional 2,370,093 sites that used Mobile Optimized historically and 944,128 websites in the United States.
Get a list of 4,030,418 websites using Mobile Optimized which includes location information, hosting data, contact details, 1,660,325 currently live websites and an additional 1,029,282 domains that redirect to sites in this list. 2,370,093 sites that used this technology previously and 944,128 websites in the United States currently using Mobile Optimized.