While C# looks like a great language, and I'm looking forward to playing with this, does Xamarin really allow you to share that much code between platforms?

In my experience, 75% of my mobile app code tends to be either working with platform-specific APIs or just quite trivial. Is the potential for code reuse high enough to justify the extra layer of stuff to understand (and potentially break)?

Edit: I can see how being able to use C# is a plus for some people, I guess I'm just slightly skeptical of the cross-platform selling point.