What startups here are focusing on developing on top of .NET?
clistctrl: 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.