Well, I do have one self-cleaning litter box.. so there's always one box that's clean here. There are also three more here. Two of them, I'm in charge of and the other is in my sister's room for her cat. That one barely gets cleaned, but the two I'm in charge of get cleaned.. well, i try to do them twice a week. I have to say, though, that Kahn will start peeing "inappropriately" if he decides the box isn't clean enough, so I try to keep them fairly clean. I also, though, put like six inches of cat litter in them, and they're huge boxes, so there's lots of room and clean litter in them. And they always have the option of the self-cleaning which is always scooped.
As far as changing litter and cleaning the litter box surfaces.. I generally will let the litter run out when I start to see little "breaky" clumps in the litter that are too small to pull out. I'll just let it get down a bit, then the next time it's low, I completely toss it (provided there aren't too many tiny clumps in there that I can't get out.. in which case I'll just dump it early).. Once it's dumped, I take and clean the litter box out and make sure there's no residue.
But, my boxes don't smell (with the exception of the "fresh" poop..) The fresh poops are enough to knock you out. I have to say, though, that cleaning them out immediately doesn't really dissipate the smell any faster than letting it just evaporate.. and once the initial stinkiness is out of the way, it's not any stinkier in the box. I wasn't sure about this, so I had a friend with a fresh nose "investigate" this for me. Gotta love friends who will smell your cat box for you. I thought maybe I needed a non-household opinion because I might be used to the smell.