I'd venture that for a well-written, non-trivial app, most of the code will be in the 'generic libraries and business objects' -- meaning that porting an app to

I'd venture that for a well-written, non-trivial app, most of the code will be in the 'generic libraries and business objects' -- meaning that porting an app to Android or iOS (if you're using MonoTouch) shouldn't be a ton of work.