This blog runs on Graffiti CMS. I have wined in the past about this not being open source and have on ocassion thought about moving it to an open source blog engine. Today I read that Graffiti CMS is now open source. I have never done a blow by blow comparison of .NET blog engines so I don't know if Graffiti is the best but I can say that it has worked very smoothly for me and has some clever built in features which I like.
This is a great contribution to the open source community by Telligent - thank you.
Source code is available here: http://graffiticms.codeplex.com/