Actually, in my experience, I'd say that while .NET is used in enterprise, it's mostly used by small businesses. My experience is mainly within .NET based CMS's, and I've worked for a few agencies and startups that build on .NET, sometimes amongst other things.

I've never really bought the argument that building for .NET is too expensive. Yes, it's a lot more expensive than free, but for a company it's peanuts when it guarantees the company a stable platform and a growing dev market. The only people that will be priced out are bootstrappers. I've built more small-business sites on Umbraco than I can count.