We found this and taking the bus to be the best ways of getting around in PV. Although the Taxi takes you directly to your destination, walking not only lets you experience the culture and stop at interesting sights, it also gives you a great workout, as before you know t you have been on your feet for hours!!! Make sure you bring water, though...dehydration is common.
Puerto Vallarta is a very walkable city. Be sure and bring comfortable walking shoes. The cobblestones are a bit difficult to maneuver with very high curbs and many potholes! You will see many Mexican women walking all over the place in very high heels....it is beyond me how they do it! They remain graceful and in balance!