Do you find people that you know popping up in your characters?
Many of my characters are, actually, lightly based on people I know. However, situations are generally juxtaposed, and several people in fact might simultaneously inspire the characteristics comprising one character. It's usually a conscious decision. Often people I don't really know (at all) help to make up a character, and I don't see how a writer can actually work in describing human nature if there is not a background from people he knows making up some basis of his work. But where it is conscious usually it's in good taste or good humor and all effort is made to not upset people I really respect. Actually I would be rather happy if certain friends read a character whose attributes were partly based on their own, recognized it, and laughed. Conversely- if someone had treated me badly, they well ought have done better else-wise I wouldn't have need write about them! And those people sometimes (as characters) perhaps end up worse than they actually are, in the fiction, but again, then - that's their own fault. I think there's always some element of using your relationships with others to create characters, there need to be reference points you understand in order to describe the psychology of a situation.