Shyness is inherently uncomfortable; introversion is not. The traits do overlap, though psychologists debate to what degree.
Some introverts are perfectly comfortable with public speaking; I'm not one of them.
What's interesting is relative levels of introversion tend to stay the same. If you went back to your reunion from school, you would probably find that if you ranked everyone in your class into terms of levels of introversion and extroversion you'd still be the same rank.
Men are more likely to be introverted than women are, but it's really very slight. But the real difference I think is in how it plays out, how it relates to cultural stereotypes.
Any time people come together in a meeting, we're not necessarily getting the best ideas; we're just getting the ideas of the best talkers.