I have used .NET for all my start up endeavors. Like others have suggested, it just works for me since I have background in .NET and windows development.

Although I have experimented with Ruby and Python both I never felt like the incurring the cost of learning curve while trying to complete a project. In my opinion my customers do not care about the language the application is written in as long as they are accessing it from a browser.

One thing I want to point out is that the monthly costs for VPS are much higher compared to linux nodes and it has a significant impact on hosting costs every month.