I was talking about the different parts of a conversation, starting with the opening, and mentioning along the way some of the ways in which the rituals differ in different cultures. The conversation went something like this:
Me: Like the British greeting All right? That confuses Americans--we don't know how to respond.
American Exchange Student: Wait, how do you respond?
Me: Let's try. (addressing a group of English students in one corner) All right?
English students (as one): All right.
English student 1: You know, it's like if Americans said You okay?
AmExSt: No, it's not. If you say You okay? to me, it means you think I look lost or upset and you're offering to help. So all these people have been saying You all right? to me and I've been thinking "What am I doing wrong? Why do they think I'm lost?"
[sound of a number of pennies dropping (variation on a BrE expression)]
So, it turns out that my strategy of replying All right or All right, and you? is acceptable. Phew.
A difference related to these different interpretations of you all right/okay? is that if you look lost in public in the US, someone will almost certainly come up to you and offer their help/directions (possibly with You okay?). In my experience, all you have to do in New York is open a map, and some local will ask to help. (I recall this happening on a subway platform and Better Half exclaiming that that would never happen in London.)
In the south of England, if you're lost and want help, you generally have to (get up the courage and pick the right stranger and) ask for help. Or stay lost, which may be preferable. An exception to this generalization would be if the stranger had some official role that makes it acceptable to address someone and offer help. It's not that help is never offered, but you certainly can't count on it. I would not be surprised to hear that this is less true in other parts of the UK, since one thing the southerners have a reputation for is not talking to strangers.
It feels to me like All right? as a greeting is getting more and more common--though the OED has examples of it going back to 1868. (Maybe I was just oblivious to it for a while.) It also feels somewhat masculine to me. I think far more men greet me this way than women, and it is often followed by the mostly masculine address term mate: All right, mate? There may be generational things going on here too--perhaps younger people of both sexes use it more? (Let me know.)
*A lot of people on the internet are writing this as Alright? Not how the dictionaries spell it--and, of course, a frequent misspelling in a lot of contexts.