If you click on the Microsoft logo, you'll be taken to the GitHub profile page for Windows Azure: https://github.com/WindowsAzure

Microsoft codeplex now supports git I believe so the general Microsoft community supports it and that specific MS product uses it now. Presumably some internal projects also use it

The ASP.NET MVC and WebAPI frameworks use Git (hosted on Codeplex.) Link: http://aspnetwebstack.codeplex.com/