I think these are just alternative titles for extroverts and introverts, but I was reading an interesting column in one of the newspapers last weekend on this topic, in relation to social networking sites.
Most of the people I keep in touch with on these sites fit into one or other of these categories. Sharing is good. Over-sharing, particularly if it's done in a "look at me" way, can be a little annoying. I'm not sure that I need to know everything that people are eating, but on the upside there are times when that information can inspire me to go and cook something I might not have tried before. When it's done in a good way, sharing can open your eyes and your mind to new things that are enlightening and stimulating.
On the other side of the coin, I'm a secret squirrel through and through. It takes a while for people to get any kind of information out of me and I'm not generally one to volunteer much. I often watch or follow a conversation for quite a while before joining in. I don't get why people feel the need to tell everyone they know on a social networking site what they just bought, what they just ate, what bug they've come down with this week etc. Maybe that just makes me dull and boring to know, but I prefer to think that it's more interesting to be a bit less out there. Hidden depths and all that stuff...