I can honestly say I never forgot a single viewing.  Of course, from when I started with TV Guide (probably around 1960) till cable crept into the picture (around '72), there were never enough monster movies on to worry about forgetting one.  In the period A.C. (after cable), I always had a piece of paper on hand when I scoured the Guide, and I made a list of times, stations and titles which I kept very much within reach.