Most of the trails are empty at night.
Two or three years ago I led an AMC night traverse of the Presidential Ridge. I was stunned to see how many other folks we saw up there at night! I suspect TJs Name is correct that most trails are empty, and if there's one exception, especially on a weekend in the summer, it's the Presidential Ridge. Not a lot of people, to be certain, but there will be someone, somewhere, hiking deep into the night, if not the next morning.
Brian