I've been playing around with C# and Managed DirectX for rapid prototyping, and I'm pretty happy with it.

It was a bit difficult to get started since the documentation wasn't that great. I put a tutorial on my website on how to get started if anyone is interested in trying Managed DirectX out.

http://www.genkisoft.com/manageddx.shtml

Developing with C# and DirectX 9 requires the .Net runtimes and DirectX 9, which is very steep for shareware game downloads.

I was using it for rapid prototyping (also for tools, etc.), and for that its been great!

It'll still be sometime before the user penetration is large enough for shareware (Windows Longhorn+ era).

Agreed. C# is by far my favourite language - it's a shame I can't use it for anything other than prototyping/tools development.