Actually, I was just sent this interesting website that covers this very question.
http://kevan.org/johari - You choose 5 or 6 words you feel describes you, and ask others to choose the 5 or 6 words THEY think describe you. You then see the breakdown in terms of :known only to yourself, known to all (you and others), and not known to self (but known to others).
I thought it was really interesting. Apparently, the whole world thinks I'm extroverted, but noone knows I'm independent. I wished for more choices... like opinionated, stubborn, determined... but it's still an interesting exercise.
