.NET may not be popular on HackerNews, or for building your startup, but step into any bank or big-business company and you'll see nothing but .NET (it has slowly been taking over the area that used to belong to Java 5-10 years ago).

It's a shame how some people view .NET as a closed platform and not open source friendly, when Microsoft has been making a BIG effort to push .NET into the open, especially ASP.NET. Let not forget things like Nuget, which has completely changed the way most .NET programmers work. Then there's Mono, which is just getting better and better every month (Host ASP.NET MVC web sites on Linux... now you can, thanks to Microsoft open sourcing MVC and Mono supporting it)

All in all .NET has become a very embracing platform for open source. I use it for just about any job, with great success.