I've always seen introversion/extraversion different to how its described here. I never thought about it as 'how social you are' or how much of a geek you are, but more like a rechargeable battery.
An extrovert recharges their battery by interacting with humans, engaging in discussion, ideas and inspiration come from their own mouth as they talk and this is why they are often perceived as the life of the party or whatever.
Introverts go out with a fully charged battery which drains as they interact. Eventually, depending on the individual, that battery dies and they no longer want to be a part of this scenario.
Charging an introvert up may involve intellectual stimulation via books or online debates or whatever, whereas an extravert strives harder to create those situations of intellectual persuit and stimulation.
As you say, it's possibly a non-scientific construct, but as a general term to describe somebody, it works perfectly well. I'm clearly an introvert compared to my sister, for example, but I'm likely extraverted compared to, well, the person I don't know because they're hiding away indoors 24/7.
I don't think it works like that with all the time. We all have our moments. For example friends of mine that want to "recharge alone" rather spend time with their girlfriend and chat online.
I have heard that model too. I partly agree with it. But I also think introverts can be geniuses at presenting themselves as extroverts for social purposes.
Bill Gates, famously
meep
Great example @mobbs
meep
Do you think Zuckerberg too maybe?