I find it somehow sarcastic that as you say "the only popular use of mono" is a platform that does not support linux.
It's in the pipeline though for Unity 4 which will be out soon (I think there is already a preview available).
They are adding Linux publishing but according to this post (http://blogs.unity3d.com/2012/07/03/linux-publishing-preview...), the editor won't be available for Linux.
Still though, this means that Mono is being used with Unity on Linux. Unfortunately not the development part.
thanks that's actually cool news. Last time I checked (half a year ago or more) I couldn't find a single hint about that.
This is the real story here. C#, as a language is fantastic, especially with the most recent versions which have added things like the Task Parallel Library, dynamic keyword, and the new async/await stuff. It's very easy to write a great performing app with C#.
Right now tho probably the only popular use of non-ms .net (mono) is Unity (which is btw a pretty big deal in the games industry).