I should add: the value proposition for mono is a bit bizarre.
On the server, typically mono is chosen because mono on linux is much cheaper than azure, or windows hosting (AWS, etc) therefore you trading slightly more development and setup effort for cheaper run-time costs.
For the phone/tablet market, you are doing the opposite trading money (monotouch licenses) to save development time and learning a new platform.
On the desktop, I think the value proposition is much less well defined. It depends alot of the mix of clients you are supporting.