I am using .NET for my startup app (nowhere near done yet so no link) which is a CRM/scheduler for service businesses. I was going to use Ruby on Rails like the other cool kids but I have more experience with .NET, my area is all .NET and I like a lot of the new things out (e.g. ASP.NET MVC), plus I am enrolled in Bizspark. I also had a fair number of issues fighting the Rails mentality (or rather, trying to shoehorn my thoughts into Rails) so I switched to .NET