Ask HN: Largest known MSSQL installation?

Having read the great article on MySQL at Facebook, I wonder how MSSQL performs in the wild. At my dayjob that's the one component I cannot get my employer to consider FOSS. Does anyone know the througput of the largest MSSQL installation? When I search the web, I can't find anything that compares to the MySQL article. Maybe that's because banks and insurers don't like to disclose this kind of information. But I keep wondering if those businesses even have the same throughput as Facebook.