Overview
I am always on the lookout for ways to improve code; short term benefits are nice but there is a great feeling in identifying potential problems way in advance, and putting in the framework early to make life easier later. Using a UriMapping when developing WP7 apps is one of the many ways you can help eliminate annoyances later.
So first of all, a brief description of how page navigation works in WP7, what a UriMapper is, and why it pays to use it. Scroll down passed these descriptions if you'd rather just see how to implement one.