Generally I don't tell them...Mainly because most people are unable to really understand even when you tell them, so there would be a lot of false assumptions and it could completely change the dynamic of the friendship you have with others.
That said, 2 good friends of mine who I trusted enough not to be too weird about it know I have HH...but even then I haven't explained anything else to them except yeah, I have HH, it's a medical condition, that's why my hands are sweating. It has been a mute issue since and that's the way I want it to be. I don't need anyone trying to check out my HH all the time when we're going out or anything, and with some people you just know that's what would happen (even if they are you're friends).
I have been thinking about telling more of my friends about the HH, but at the end of the day, it doesn't really help the real problem (HH) and creates a lot of weirdness I don't need.
As for jobs (where it's more of a rational business decision); it's kind of a double edged sword...in some cases you might be able to spin it as an advantage (look, I have had HH all this time and I'm still here) but sometimes it might also be a disadvantage (illness isn't something most 'robot' interviewers are looking for, in the cold hard real world). I guess it depends on how you think they will regard HH, and how it would apperently affect your ability to do the job (obviously, some things like sales etc will be tough). If you're thinking about an ethical dilemma; I don't think there is any duty to tell them, as long as the medical community refuses to see this as a real problem...
