In fact, Microsoft should support Mono. And it does something now! Mono project now has something called Moonlight runtime which enables Silverlight on Mac OS and Linux. Also there is a Lunar Eclipse project to replace Expression Blend.
More and more Linux distros start to support Mono, such as SuSE, Ubuntu, Debian, and Red Hat which makes Mono a much more well known runtime. So IMHO it is time to test your .NET applications to see if they are Mono compatible.
It is a pity that SourceGear Vault clients (command line and GUI) is not officially Mono compatible. Because Mono has implemented most of Windows Forms, a test would not be so hard.
I have tested CBC but the result is really useless. Why? Is there going to be a RAD Studio for Linux?