My own startup uses C# and the MVC framework. I also have a windows service (.net C# as well) for some data processing. My main reason for choosing it was development speed (it is what I know best) At my day job I work for a consulting firm that does sitecore CMS implementations for large sites. In addition we developed a CMS for displaying data visualizations for data oriented sites. The biggest benefit of .net for me is the tool set. Visual studio is very solid, intelli-sence makes me a productive programmer, and plugins such as Red Gates Profiler make me a fast debugger.