I think most Apple Watch use will mirror iPhone in terms of etiquette. It is common sense to make sure you don't look distracted during important meetings or conversations.

People might find it hard at first to ignore their watches. I'm not sure how notifications work entirely yet, as in will they illuminate the watch face when they send their tap or will it just tap until the watch is raised? If it's the later then people might unconsciously look at their watches from a tap but should learn to ignore it just like their iPhone.

It all depends on the situation. We won't mind if our friends might text every once in a while as the need arrises, but if we are directly talking to someone it could be irritating. I would find it incredibly irritating if I was at a restaurant talking with a friend who kept glancing at their Apple Watch, because I knew they were looking at notifications. I might ask what is so important because I know the nature of their glancing.

Large meetings or dinner parties might be interesting. I know dinner parties have made games out of phone use and had rules that whoever used their phone paid for everyones dinner. Meetings will be tricky since generally everyone wants you to be taking notes or paying attention, unless you're looking up information for the group. If that is the case the iPhone would be better for looking up information and the Apple Watch would be a flashy annoyance because you'd have to voice your question instead of quickly typing it up and getting multiple results that could be copied and shared in email.

Public might view might be different. It might be a bit concerning at first to see so many people staring at their wrist for so long. We are used to someone in a commute like setting making many glances at their watch but to stare at it might take some getting used to. Oddly enough I might feel more comfortable interrupting someone staring at their watch than their phone.

School will be the worst. If high schoolers get the Apple Watch then teachers will definitely have to keep an eye on them. College might not be as bad except during tests which could get difficult.

I'm not sure if this will make the general social disconnect better or worse. I read Wired's article about their original intention to be less disconnected but I don't see how that will help except to force users to weed out important notifications. Sure by only looking at what's important you'll be looking less, but most people already know how to do this or don't care. I don't let Facebook, Twitter, or Instagram do any notification updates on my iPhone. I do want to be notified when my girlfriend texts me she wants me to get more milk when I'm at the market. Overall I think it will be the same as a smart phone, people who have no manners will do what they want and the rest of us will try to act appropriately to the situation.