3 or 4 times a day sounds good, but if I were to be held to that answer for the rest of my life- day in day out- then I'd have to say... once or twice.
depends on the person. I've slept with girls that I'd never sleep with again. And I've been with girls that make me want to do it all day.
It also depends on how long you've been with your partner. It's like buying a new game for your console. You play it to death untill it gets repetitive and then you want to play something else. Unless it one of those amazing games that you can't get enough of, but they are rare.