It depends on budget, interest, and also the field you're going into. For example, I know colleagues in humanities who applied to 7 or 8 but for the people I know applying to Health Informatics, the standard is 3 or 4, maybe even less if you know exactly what you want.
I was browsing this forum while considering whether grad school was right for me. I just applied to my dream program a week ago and now I'm back to just take a look, see how others are doing, join in the misery that is waiting for decisions haha.