Strong examples of tech startups going (or staying) with .NET?

I am looking for specific examples o开发者_JAVA百科f vibrant, acquirable (or acquired) tech concerns, especially startups, that chose to build on the Microsoft stack and either succeeded or appear likely to.

Writely is an obvious example, as is NewsGator, PageFlakes, and StackOverflow itself.

I don't mean this to be a language debate. I hope the question is not too subjective for SO; I and the team I work with have benefited greatly from the solutions to coding quandaries that can be found here, and I expect that the people who could best answer the question frequent this site.

To make the question a little more specific, let's say you are a .NET expert and a member of a startup who is at a turning point. That turning point may or may not involve a shift in platforms. Avoiding subjective arguments, what quantifiable examples - companies or case studies - can you point to in favor of going or staying with .NET? (Extra points for examples in the Valley.)

I'd recommend looking at Microsoft's BizSpark startup directory.

This shows most of the new startups taking advantage of BizSpark (which will be any that are intelligent, using Microsoft technologies). Most of these are likely .NET oriented.