We do laundry one day a week. My daughters have an assigned day and they do all their own. So basically it happens 3 days a week at my house, but I have an awesome husband who does our laundry, so I never have to do it.
Usually once a week if I have been going out a lot if I am at my house just sitting around then every 2-3 weeks since I have enough undies and shirts to get me through since I wear very little at home.
I'm pretty terrible about doing laundry. It tends to be once a month or so for me. I have a ton of undergarments, so I can wait until my hamper is overflowing to do laundry. I usually resign myself to laundry when I realize I don't have any jeans or work clothes left.