You can share significant amounts of code and design, but WP8 will necessarily require departures from the W8 app in UI design. For example WP8 uses panorama an

You can share significant amounts of code and design, but WP8 will necessarily require departures from the W8 app in UI design. For example WP8 uses panorama and pivot controls, which are not available in identical form in W8 (although analogs do exist).