My imdiate family knows the full extent of my SP... after all they are the ones who took me to a doc. SP and certainly shyness is not a concept alien to them.
As for extended family, (well the ones that I see relatively regularly), some probably suspect I am different (ie can't hold a conversation, don't have many friends etc etc), but I haven't talked to them about it.
As for my own friends, I have only told three of them about it and both times it was while I was drunk. I haven't told any of my school or uni friends although I did admit to two of them once I did take meds, but I didn't elaborate.
For the most part, I try to hide the problems I have, but sooner or later they realise the sort of person I am. Sure most don't know my problems by the name Social Phobia, but I don't have to tell them that I don't have many friends, I am extremely shy. At times I feel so transparent.
-SS