Our household is kind of a mix of the replies in this thread so far.
We have 3 boys, and their clothes are washed after every use. Not a single article of clothing we put them in can avoid food, mud, sweat, grass, marker, snot, sunscreen, bugspray, or pretty much anything you can think a young child would touch. After a week, we have at least 3 loads of just their stuff (and it smells absolutely atrocious).
My wife insists on washing her stuff after every use. We split the laundry duties 60/40 (weighted toward me), and I can usually sneak at least her jeans and bras back into the closet a few times before she notices.
My stuff gets more use - shirts, socks, and underwear are washed after each use, while pants and "sleep shirts" get a few days before I bin them.
I wash my jeans about 1.2x a week. I end up getting them pretty dirty after 4 or 5 days because they're my work pants. I'll typically spend the whole day in them, and I am not supposed to come to work with stained or soiled pants (can't avoid it if the stain happens at work).
That being said, we do wash about 70% of our stuff in cold water. Socks, underwear, and hand towels/washcloths get the hot water, especially soiled stuff gets warm, and the rest gets cold. At least half our stuff is also line dried, saving a lot of money on the dryer (and the integrity of a lot of our clothes).
I know there's a lot of unnecessary clothes waste out there, and cold water/line drying/prolonged wear cycles are key to keeping clothes longer. There's a finite point though, my jeans all regardless of brand or fit wear out at the crotch and knees at the same time. It's not just one small patch either, towards the end of their 'life', the whole thing is practically see-through. I've heard all the arguments that you can patch them as needed, but I challenge anyone who says that to fix my pants without just cutting the entire crotch out and re-sewing a new one on.