I think it's important to define "extrovert" versus "introvert". My current understanding is that extroverts derive their energy from being around others while introverts do not. Introverts are not necessarily shy people however, after being with others in social situations they may feel tired or as if they were working hard.
Based on that understanding, I'd say I'm more of an introvert by nature. I definitely enjoy the company of close friends and can get quite loud however, after a certain point (often earlier than others), I seek time alone or a break. I certainly feel this much sooner if I'm in a newer setting around people I don't know. I definitely feel more sensitive around people in larger groups.