I think Mono, and the C# language, are a great, nay, fantastic project.
My question is: how prevalent is Mono in Ubuntu? How much of a penetration is it getting, and what applications run on it?
There are a good number of programs that use mono in Ubuntu if you look at the whole repository. In the default install, I believe the following are the only mono apps:
There may be more, I just made this list from looking at which applications would be removed if I removed libmono*. However, even just having these means that a good portion of the mono framework is installed by default which makes it very easy to deploy mono apps onto Ubuntu. A few very popular Ubuntu applications are written in mono, including gnome-do, Banshee, and docky. The trend I've seen from the sidelines is that despite its detractors, mono is gaining a lot of ground with Desktop application authors because of the speed at one can develop fairly rich GUI apps with the monodevelop IDE.