I recently realized that I pulled the latter and based a character off of Thomas Jefferson, Leonardo Da Vinci, and other random Renaissance Men. He's the exception rather than the rule, however.
"Jack, you have debauched my sloth."
I actually build my characters from: (a.) traits I find interesting or appealing (b.) Bits of myself (c.)Bits of OTHER characters of mine.
If they end up resembling someone close to me, it's usually an accident.
Occasionally Smart
Me too, I've only ever based two characters on people I know and that was intentional. Otherwise, my characters seem to come from nowhere. I rarely ever sit down and think "Okay, I need to come up with a character. I want her to be like this, and this and this..." Character concepts usually come to me half-formed and then I tweak them, adding traits and removing them as I think is necessary.
He's like fire and ice and rage. He's ancient and forever. He burns at the centre of time. Rory punched him in the face.
Exitus Acta Probat
I have sort-of base characters on real people, altough not often. Phil from Forgotten Lore shares some traits with me, but his personality isn't very similar. He's more of a generic geeky guy than a self-insert, but since I am a geeky guy, he ended up with lots of the same traits. Zaran from Forgotten Lore is also essentially a combination of two characters from an earlier version of the story, one of which was based on a real person. The final result doesn't really have much in common with the actual person, beyond some very basic traits (they're both cheerful and impulsive). If I was doing something with voice acting the similarity might be noticeable because I picture Zaran having a similar, rather distinctive, way of speaking. Also, I did name one character after my friend. Well, perhaps a character isn't really an accurate term, as it's more of a case of one of the characters mentioning the name of his friend who doesn't actually appear in the comic at all. I didn't bother to spend a long time trying to come up with a good name so I just used a variation of the name of a real-life friend.
I've taken traits from people I know—mainly different bits of myself, which should explain their serious issues—but never have I either based a character off of someone I know directly or actually been pressed on the matter. Which I suppose is a good thing on several levels.
I'll hide your name inside a word and paint your eyes with false perception.