I am not old enough to see the original when it came out waaaaaay back when, but my grandparents had HBO, Showtime, and Cinemax and went to bed early. That movie freaked me out, and made it almost impossible for me to take a shower. (Baths were fine as the shower curtain could be left open) To this day, when I think I catch a wrong shadow while standing in the shower, I am ready to deliver a naked beat down to whomever might possibly be standing outside the shower. I mean when are we any more vulnerable than when we're standing in the shower, naked, with nothing to defend ourselves but a bar of soap and a wet wash cloth...and a back scrubbed if we're really lucky. Alfred Hitchcock was a bloody genius, and I have to hand it to him for mastering the art of messing with the mind.
Also, on a side note, I agree with Poltergeist as well. My cousin thought it was a great movie to take me to see as a kid. :O That clown just creeped me out. Then as the trauma started to pass, I read Stephen King's "It", and yeah, yeah...killer clown in a storm drain. Clowns to me are creepy anyway, but neither of those helped me out a great deal with that perception.