I am able to deliver features and fix bugs faster when programming in C#.NET and ASP.NET MVC. I am able to administer MS Windows Server with my eyes closed. SQL Server too. That's why I chose MS technologies for my startup. That's what I know best. Use technology that you know best. You wouldn't use a language you hardly know to write a book. You wouldn't want to experience with a second language. Why on Earth would you want to use a sexy and cool tech that you hardly know?

The most useful piece of software that is used by almost all Software Developers around the world was created using Microsoft.NET -> That piece if software is StackOverflow.com. Microsoft .NET is not a sexy and cool tech. Solving problems is hard enough. Don't make it even harder by chosing technology you hardly know.