This is something I have thinking about quite a bit lately, as I plan to get the sleeve in May. So far only my (very supportive) husband, and my mother (who had RNY 4 yrs ago) know. As far as telling others, I think I will decide on a case by case basis.
As someone else pointed out, those who have not been overweight all of their lives cannot understand what it is like to try diet after diet, to exercise and count points, calories, carbs over and over again, only to fail, and usually end up a few pounds heavier in the process.
So I think that if people ask how I'm losing so much weight (assuming I do LOL) I will simply reply portion control, and exercise. If someone who I know has had a similar struggle with their weight asks me, I may divulge the information, but for friends who have always eaten what they want with no consequences, I think it's none of their business.
Another thing I am struggling with is what to tell my job(s). I am an ER nurse, and my surgeon told me no lifting more than 10 pounds for at least a month post-op. Now, generally I don't lift an awful lot at work but my job description says I need to be able to lift 50 pounds... do I tell them I had surgery, and need light duty? Or do I just take the month off for personal reasons?