Okay, it's a lame excuse, but I found this list of myths about introverts interesting:
I'm surely an introvert myself.
How does this apply to writing? It's easy sometimes to make all the characters do what you would do in a situation, but that doesn't feel real, and would make a boring, flat story.
In Meskka, for instance, Tomed and Bast are extroverts, and Nilre is an introvert. Rrrark is more of an introvert, but he can be outgoing if he has to be.
In An Unwanted Apprentice, Kendra and Alenk are introverts (it's a bit of a cliche to have a collage researcher and student be introverts, but that's a different topic...) Tannin is definitely an extrovert... and not just because he won't shut up. ;)
That's just one of the fun things I like about writing, exploring different personality types.