This article does not go into much detail. I believe the Mono project is more complete and has a larger developer community and it does not have a current and complete implementation of systems like ASP.NET. What they can implement more readily are the C# and CLI standards which are publicly documented. A full ASP.NET, WCF and LINQ implementation that runs on MacOS X and FreeBSD 7.0 would be great though. I personally run both FreeBSD and Windows servers for different purposes. Being able to drop some utilities on my FreeBSD box is something I do want to do. And simply having MSBuild run on FreeBSD and Windows would be a huge asset.

For cross platform use Mono: http://www.scribd.com/doc/244387/CrossPlatform-NET-with-Mono?ga_related_doc=1