For another approach to this problem, see the Urbanspoon iPad app. It shows every restaurant in a city, drawing them as dots in a map overlay then swapping for

For another approach to this problem, see the Urbanspoon iPad app. It shows every restaurant in a city, drawing them as dots in a map overlay then swapping for pins when you zoom in enough that a manageable number would be shown. This doesn't deal with clustering, of course. It's a different UI solution.