Both personally and professionally, I write C# daily for Windows forms apps and Windows services. Even after years of this, I find it FAR faster to whip out a web app with PHP or Python than to do it with .NET. Maybe things have changed with Silverlight, but to me the learning curve on ASP.NET is ridiculous compared to the payback.
Edit: The above was written a year or so before I tried ASP.NET MVC. I find ASP.NET MVC wonderfully intuitive and clean.
