Hmm, good question.
PSI - I've played through to Baya Malay countless times, but then I'm usually intimidated by that massive tower and then I stop.

If I had to guess, I'd estimate I've beaten DarkFalz about 5-10 times.
PSII - I love the idea of this game on paper, but I have no patience for the actual gameplay. I really think I've only played it all the way through 3 times.
PSIII - I know I played through to all four endings (without cheating with save states

), and I've gone back a couple times, so maybe 6-10?
PSIV - more times than I can count.
PSO - I've done the first three difficulty levels with my main character, the first two with another character, and I have two more characters that are almost ready to finish "normal" mode.