I'm not too familiar with what Guthrie has done for the .NET community, but Hanselman is a famous proponent of open source and making .NET as fun to code in as ruby and python. His coming to MS has changed the way I look at the .NET stack.
And let's not forget Phil Haack (http://haacked.com), who is now working at GitHub. He used to be the program manager at Microsoft for ASP.NET MVC, the first part of the ASP.NET framework to be released under an open source license.
Yeah ScottH has done a great job. ScottG hired him, plus a bunch of other community advocates over the past few years. Some have since moved on, but MS really did a great job of listening to devs who build on MS platforms.