We've considered doing the same thing at our startup. I'd love to hear more about your experience. Did you simply build a node.js UI server that made calls to a C# service that did the database accessing and business logic? Or did you cut out C# all together and access the database and perform business logic directly in node? We're worried that re-writing major components in node would slow us down too much at the moment, but I'd love to hear your thoughts on the productivity boosts you found.