i agree with KatyaWiccaUK, you have to choose the right time, and tell the right people. when i decided to convert, i first told my mom because we were close and i didn't want to lie to her. she accepted it. with my friends, i forget how i told them, but it was some time later, i think my one friend said he was Wiccan and i was like 'no way, me too!' as you get older that's kind of how you come out of the broom closet i've noticed. there's many times where i'll bump into a stranger, or a friend of a friend, and see a pagan symbol, and next thing we know, we're talking about our craft.
i'm half in, half out. i don't go around proclaiming my faith, i do wear a dragon pentacle every day, and people have commented on my necklace [i wear in interesting necklace with some other things on it] there have been some times where i knew wearing it would be a bad thing [certain job interviews] but i never take it off. if someone asked me if i was Wiccan or what my faith was, i'll tell them without hesitation [unless they were holding torches] but i don't see a point to introducing myself like 'hi, nekoshema, i'm a witch.'
there's been one or two rough patches at the hands of people i don't know finding out about Wiccans/Witches in the area and having a big freak out, but my friends and family don't really care too much. i haven't told everyone, because i know some would be upset, so unless they ask me, i'm not going to tell them.
there are instances where not telling someone is the right idea. people in Africa are being killed for being witches [or accused of being anyway] not too sure if people are being killed in the US or UK but i know of places being vandalized, people being assaulted, attacked, and many people's works will fire them. wait for the right moment, and if you get a gut feeling something bad's going to happen, don't speak up. you have to decide for yourself if you should come out or not. just be sure if you know who you tell will freak out, figure out the best way to tell them to soften the blow.