Also porting is interesting - we're in a position where we have a bunch of highly optimized, debugged C/C++ 'backend' code. Since native code isn't supported on Windows 7 Phone, we'll have to port our app by rewriting it all in C#. Unfortunately, it's not practical option for us at the moment.
I'm going the other way - my own code is all in C# (Mac and Linux with Mono, and MonoTouch and MonoDroid for the mobile platforms) so deployment to any of the above platforms becomes relatively easy. (I'm writing games, so I can hoist a lot more of the otherwise platform-specific logic into OpenGL, OpenGL|ES, and XNA, respectively--still requires building different GUIs based on desktop vs. phone but is a lot nicer than Windows vs. Mac vs. Linux vs. iOS vs. Android.)