I don't really do this, but I can relate to what substitute was saying about being a "utility person" for friends. I'm good at catering to people. Now, sometimes when I'm talking, I might exaggerate something, but it's usually meant in a humorous way. Others might assume I'm being serious, but I'm probably not. If I'm talking about facts that I'm not sure about, though, I always back it up with "but I'm not positive about that." I'm too paranoid that it will come back to get me, and there's nothing I hate more than looking incompetent after acting confident.
Strangely enough, the biggest compusive liar I've ever known is an ISTJ friend of mine.