As opposed to dividing the human population into three groups consisting of introverts, extroverts, and ambis?
Well I don't think the introverted/extroverted ness thing is a division...I think that's more of a scale that people fall on. I think while people might sit more often at a point on the scale, we generally slide, moving around as outside factors influence which is exhibited. (As said by many others on the thread, social anxiety can often make people seem more introverted than they otherwise would be. Likewise alcohol can make people seem more extroverted than they otherwise would be.)
I've been thinking about it with this thread and I don't think I could pin myself down as one or the other. I now think that there are very few people who are absolute introverts or extroverts. There are times for most of us where we draw energy from others, even if it is only online. And many times when people draw energy from being alone. At this point in the thread reading what others have said and having thought about it a bit more, I don't think people generally are one or the other. I think we mostly occupy one place on a scale which can change due to outside factors.
But yea, I tried the personality test on myself and ...nope, didn't fit me at all. It reminded me of reading a star sign.