Sounds like it is official. With the release of Mono 2.4 and MonoDevelop 2.2 we now have support for developing ASP.NET MVC Web Application on Mac OSX.
The Mono 2.6 Highlights include:
- This release includes Microsoft's open sourced ASP.NET MVC, ASP.NET AJAX and Microsoft's Dynamic Language Runtime.
and the MonoDevelop 2.2 Highlights include:
- ASP.NET MVC support, you can now develop, debug and build ASP.NET MVC applications from MonoDevelop.
- New T4 Macro processor (Text Template Transformation Toolkit) integrated directly into the IDE (Mono's T4 is also available as a reusable library for use and abuse in your own programs).

Gotta try this out! Learn more here.
David Hayden
Filed: Microsoft .NET Developer Tools
ASP.NET MVC Web Development