We just introduced Backfire, an open source javascript engine that allows you to save CSS changes made in Firebug and Webkit inspector to the server. The library includes an example C# implementation of how to save the incoming changes to your CSS.
Here's a blog post about how it works:
http://blog.quplo.com/2010/08/backfire-save-css-changes-made-in-firebug/
And here's the code hosted at Google Code:
http://code.google.com/p/backfire/
