I always scoop the poop on walks. But in my own yard it is one/two times a week in the winter and everyday or two in the summer. I don't like the small of poo. Ziva's poo area in the yard just happens to be right outside my bedroom window. So, in the Spring when windows are open(ie: now) I clean everyday.
I voted once a week because it depends on the time of year. But once a week at the minimum.