I was just thinking this as I was reading through the thread. When I was young, before cell phones, everyone honked.
I wouldn't do it now, but mostly because I'm so accustomed to texting. But I don't consider it rude. I don't think a quick honk is really any more disruptive than any other normal neighborhood sound.
I don't get too annoyed by a quick honk, it's when they sit in the driveway and honk, and nothing then honk a little longer, then lay on the horn, then honk again. All I can think is get off your lazy ass and go to the door and drag your dumb ass friend out, or find out what's holding them up, because obviously your stupid horn isn't doing the trick.
These two basically summed up my thoughts on the matter.
Personally, I don't honk, not because I refuse but because I rarely have a need. If I'm the one going to pick someone up, I'm the type that calls to let them know I'm on my way. Which means that most of the time, they are already there and waiting when I arrive, especially if plans are time sensitive. Otherwise, I just walk up to the door.
I don't find the quick signal honk to be rude or obnoxious at all, though. I wouldn't be offended if someone beeped the horn to get my attention. We have neighbors that do it, and while I do notice, it really doesn't bother me. (It's a family with a handful of preteen/teenage kids so there is a lot of drive up, drop off one kid and drive away with another for various things.)
And I do have the couple of friends that I probably would honk at in a hurry (I haven't had to, but I would), because I know their cell phones always have the sound turned off. Or they have a dumb alert/ringtone that they NEVER hear. LOL
ETA: I submitted "sometimes' on the poll. Again, not because I do, but because I wouldn't find it rude to do so. lol