I use iscore, but agree that it is hard to pay attention to pitch location during game. However, I record all games from behind the plate and now score all of them from home after the games. I can score a 2 hour game in about 30 minutes. Can freeze the video of the ball coming across the plate easily. Not an exact science, but relative. I tape a piece of transparency paper on the screen and sketch the strike zone with sharpie (first tried dry erase on the screen....don't do it).
Im thinking about building something like this into my stat tracking app or maybe even creating one as a standalone app. What all are you looking for in the app?