I doubt that most users will notice or care what the URL they are visiting is until they need access to it, e.g. for bookmarking, or for copy/pasting into an email to send to a friend "John! You like Ninja Monkeys. This page has the movie DVD for only Ģ5!". If the URL to the page they are actually interested in is masked, then you wreck things for the user.

There is nothing stopping you rewriting all URLs so they take a nicer format. Even if the user performs a search using a form, you can have form handler redirect to a prettier URL.