Super Mario Bros. 2, Mega Man 3, Super Mario World, Zelda 1, 2, and LTTP, Super Castlevania IV, Final Fantasy IX, Okami, Beyond Good and Evil, Braid, Limbo. Those are about the only ones I can think of through thirty years of gaming, though I may be missing another NES title or two.
So, not very often at all. Less than 10% I'd say.