Ele, excellent point. Despite scoring 100% extrovert on the tests, I do have an introverted streak as well. I need large chunks of alone-time every day, to recharge my batteries. I do, however, crave company of people and get energized by it as well. Very strange how it can be both things, huh? And... this made me just realize that's why I love participating in online communities so much!! I can socialize with people - from the quiet solitude of my own home.
Also, growing up, I always thought I was introverted. The reason? Compared to my brother and sister, I was a wallflower and quiet as a church mouse. My siblings are EXTREME extroverts. They can be overwhelming. When we all get together, you can't get a word in edgewise and an observer would think I was introverted.
I also want to add that I think there's way too much emphasis on the E/I distinction. That's not the most interesting part of temperament, at least, according to Keirsey. What's more interesting is whether you are an N or an S. This is the first "cut" - so to speak. It rarely changes as you develop through life, whereas E vs I tendency can, and P vs J can too. Even T vs F can morph.