If its a pretty well packed bowl, i'd say about 5 good hits, but after that there is still more but it just tastes pretty bad. Once it starts to get really ashy on top and the hits taste really bad and come out small, it's beat.

Pipes give you a lot of smoke and are probably the most efficient way of smoking your cannabis, but if the smoke hurts your throat too much after the first hit, I would suggest investing in a bubbler or bong. Bubblers are smooth and more convenient than a bong, but there's nothing like a huge bong rip.