yes but you need to re-compile it against mono which does work on the mac. Do a search on 'visual studio lite' in google.

Yep as LynxSi says its typically your dependancies and certainly any database access is going to cause an issue if its local rather than remote. Mono has limited support for cocoa. ObjectiveC is a superset of C so if you aren't relying too heavily on the .net framework it would be possible to make code changes and compile in Xcode but you would have to rebuild the UI using Interface Builder.

As a developer, I always use a language that is platform independent, which in my case in Python. You may not be a Python user, but writing your app in C# will definitely make it not portable.

Instead, use one of Apple languages for it.

Good luck

It won't run natively, but you could use Parallels or VMWare on the mac to run windows and your windows app.