I can't imagine going only once a week. That sounds terribly uncomfortable.
Generally, somewhere between two and five times a day. Depends on what I've been eating, but I consume a lot of fiber in the form of smoothies, so it's usually pretty regular.
My boyfriend, on the other hand, eats a very standard American diet when he's here in the States and goes once a day. Always in the morning, right after his first cigarette of the day. He got a new job a few months ago at a cafe where he cooks with lots of vegetables, couscous, fresh breads, etc. and after a few weeks he complained to me that he was now having two bowel movements a day and that they were "different" (after this conversation I said "So... why did you tell me this?"). I told him that a change in diet can do that, and his response was "Oh. I guess I'll stop eating at work, then."
He's back to a diet of chicken sandwiches and beer and his bathroom habits have returned to normal, or so I'm told. He probably would have been better off adjusting to a new toilet schedule and keeping the healthier diet...