Want to ship to everyone, Forget it in most cases.
All this talk about “code once deploy anywhere” is rubbish… if you have written software for a Windows PC, chances are you will find some incompatibilities with Mono and even with the compact framework, So, no, its a pile of rubbish, if someone in defense tells you that it needs minor adjustment’s, In many cases porting C++ software from windows to Linux has been easier, to give you a taste, download the Mono source code and then imagine that you need to make changes there not in your software.
In short, If this is one of the advantages you are looking for, cross this one out, OS-X and linux will never run Windows software like you would like them to, change is almost always a must for a sufficiently lage project.
Much of the stuff you would hope will run on Mono are patented by Microsoft, Meaning no one will ever implement them on other platforms.