Not often.
Mantanace,neighbors,UPS,friends…
A minimum of once a month, but that’s the bug person the property manager contracts with. Other than that, maybe once every other month, usually trainee folks fro the AT&T place up the road trying to sell UVerse, without knowing that’s a company I’ll never do business with again (I’m never mean to them, just explain that I’m not interested-it’s not these folks fault that the company screwed up big and wouldn’t make any attempt to fix it).
Back in Tucson I used to get occasional Mormon and JW folks, but not here.
After saying we rarely get unexpected knocks, I got one yesterday. A couple of men from a local Baptist church were inviting us to a special service they were having. They handed me a flier and left. I was prepared to turn them away because I was in the middle of jam-making, but it was quick and painless, and their flier went into recycling. Easy-peasy.
4-5 times per DAY. Most are friends of the kids looking to play or asking them to do something. We get some sort of sales person almost daily-roofs, windows, cable, landscaping, mowing, fence/deck, driveway coating, True Green, autism fundraising, suspicious candy charity stuff, LDS, Rod Parsley.
Never - the dogs are already barking and the person will call from outside the fence. If it’s not the neighbour it’s the Jehovah’s Witnesses. Anyone who’s calling to visit will call first to make sure I’m home and my furry alarm system will kick in when they turn off the main road about 500 yards away.
2-3 times a month, almost always a religious org. or salesperson of some sort. We have a large glass window in our front door, so pretending we aren’t home doesn’t work. 
Maybe I’m a dick; I figure as long as I’m the one paying the mortgage, I can answer the door or ignore the person as I wish.
I live in a house in a quiet neighborhood. In the last two years, I’ve received only one knock on my door while home. I didn’t answer and I never would.
Almost never.
Yesterday a Democratic canvasser knocked. I was in the kitchen cooking bacon for BLATs, so I didn’t go to the door. Just talked to him through the screen.
Last month a neighbour had locked herself out of her cabin and asked to use the phone.
Two or three times a year (each) I get religious people (usually JW) and sales people (usually vacuum cleaners or carpet cleaning).
Never, in the past year or two. Several years back we had two salespeople knocks to get us to switch cable providers and not again since. UPS and the like refuse to knock and instead just leave “Failed to Deliver” slips, and the food delivery people call us instead of knocking. We’re in regular old suburbia.
Family and friends have always set up a date ahead of time and we’re ready at the door for them.
I’d kind of prefer it if the postal people knocked, especially in the years we had someone home to answer the door and sign for the package, but what can you do.
So if someone is knocking on the door it’s inevitably someone I don’t want to meet. In one case, a drunk guy with the wrong house who proceeded to knock the door in completely! :eek:
Pretty much only for deliveries. And pizza. I always answer when it’s pizza!
Oh, and the cops came by one morning about 2:45 looking for a prowler - I answered that knock too. :dubious:
It is interesting that some people are pestered frequently by religious missonaries and door-to-door sales people. I haven’t seen either of those in years, and can’t think of a time when it was common to see them. Maybe I’ve just lived a charmed life…
Oh, yeah. Pizza guy knocks at the door. But it’s cheaper if I pick them up, and half the time I make my own pizzas; so not many pizza deliveries anymore.
UPS, FedEx, and (occasionally) the mail lazy knock if we’re getting a package.
I didn’t count deliveries since I expect them.
I put a brass ‘ship’s bell’ next to the front door. (We don’t have an electric or manual doorbell.) No one ever uses it. 
Pizzas a weird one for me. I tend to pick up because both places I order promise delivery “within an hour” but are only a block away, so it’s quicker to walk over and pick it up. But one of them doesn’t deliver to my street (according to their computer), despite being around the corner. Maybe just fighting laziness.
I can’t even claim pizza deliverymen, because they’re not allowed into the building. We have to meet the guy downstairs.
I’d say we get a knock most days that we’re home for a substantial chunk of the day. Most of the time, it’s neighborhood kids looking for someone to play with. Sometimes adult neighbors pop by to return things they’ve borrowed. Proselytizers and sales people aren’t terribly common - maybe once a month.