It all depends on whether I know them at all and/or how well. As you probably remember the entry to our flat is small and cramped...

I think ushering someone in past you and then closing the door behind them can be more overtly welcoming, so I'd probably be more likely to do that for more formal occasions, given space. For friends just popping over I wouldn't bother.

I'm middle class/white/female/early 30s, but can't see anything of particular note in that.

Actually, yes, the better I know someone and/or the more often they visit, the more likely I am to expect them to do door-closing themselves. (so Marna, for example, barely even gets the door unlatched for her & does the rest herself ;-) )

i think the only time i don't close the door myself is when i've been interupted from whatever i was doing atm and have to get back to it. so usually it's sommat like 'oh hi! close the door please, sorry but i've gotta do ' and then either i yell at them to come into whatever room i'm in or i'm able to rejoin them.

but i don't think it's because of any way i've been raised. think it's probly just me being the control freak that i am :P

It depends on who it is and how well I know them.

Generally, if I know someone less well I would expect to close the door behind them on inviting them into my flat. People I know well I would encourage to close the door themselves, because they're closer to it and it's more friendly (IMO). If there's someone who is expecting me to close the door I'd normally do it to match their expectations.

If I'm going into someone else's house and they don't make moves to close the door behind me I normally ask 'do you want me to close the door or leave it?' in case it's deliberately left open/ajar/locked in a particular way.

If the door is stiff/otherwise complicated I'd expect the owner to deal with it. If either party find closing the door physically difficult I'd expect the other person to at least offer to do it.

The logistics of letting someone past me in a confined space and then closing the door behind them while still facing them / talking to them / paying attention to them (which seems like the polite thing to do with a guest) always seem incredibly awkward. I'd shut the door behind me when I came into someone else's house, & when I let people in I default to expecting them to close the door (I mean, it's just a question of pushing it shut behind you, you can carry on talking while you do it, and it's something I'd expect people to have experience of doing without even thinking about it in their own house -- it's not like I'm leaving them to struggle with unfamiliar controls for a space-age airlock). But then they just leave it standing open, and I'm left to struggle past them, saying "Um, let me just, you know, shut the door". It's baffling. Do these people normally leave their own front doors standing open onto the street? It's not a huge thing to ask of a guest, to shut the door behind them, is it? But I'm now wondering if everybody just thinks I'm horribly rude because I don't close the door for them. A whole new world of etiquette anxiety opens up before me.

I would normally close the door for visitors, but that's just in case they have trouble doing it themselves: for example, the latch on our current door is a bit finicky and I wouldn't expect a visitor to know that you've got to turn the knob to convince it to close properly.

I generally assume that it's polite to follow the other person's lead. So, if someone holds the door open for me (rather than opening and letting go), I wouldn't try to close it, but I would close it if I was the most conveniently placed person to do so. I wouldn't be at all offended if they then went to check that it was properly closed/locked as doors can be fussy things.
The same holds if I'm the "host" - I'll let the guest close the door if they seem about to, or do it myself if not. Although currently I do have to wait for them to exit the hallway to do so whether they have closed it or not, as it blows open if left unlocked, and is tricky to lock even if you do have a key.

It really depends. When I'm answering the door, if it's someone that I'm comfortable with and has been over many times I'll open the door and just let them in. My closet is right next to the door, and I find that letting them in and closing the door behind them usually involves maneuvering that I'm sure nobody involved really wants. In my experience other people treat the situation in a similar manner.

Of course if the person is carrying something or is otherwise unable to close the door then that is a different story. ;)

I think it depends quite a bit on the physical surroundings of the door. I also think it's also a bit different if there are two of you greeting the person in question. This sort of stuff that you do without thinking, is surprisingly hard to figure out.

Our door tends to slam shut anyway, especially if there's a window open somewhere else in the house and the draft blows it shut.

I've always let the people past me and then closed the door. It was the way I was brought up. After the "Stamford Hill" incident where I was assaulted and robbed at knifepoint in my own flat after someone kicked their way through my door as I was closing it I've been especially sensitive to front door security.

I always close the door myself. With all due respect the chances are I would be able to deal with someone trying to force their way in more that most of my guests. Not so much that my physical strength would ness be stronger but that every time I close a door I am braced for someone to kick it in.