It depends on the company you're around, and extraversion isn't only limited to people. It's an outward focus on the external world. It applies to external activity in the outside world that is not associated with people, also. Take ENTPs for example. They're extraverted, but from what I've gathered, they're not extremely dependent on other people for energy. Their focus is on interaction with the outside world in general through their extraverted intuition.
One way introverts are described in one book I read was as having a "mind blank" effect in conversations. Other introverts may not experience this or may experience it on a different level. I know at least when I'm with strangers or a large crowd of people, it takes me 20 minutes just to formulate a complete thought. However, if I'm with my immediate family or close friends, I'm completely relaxed and just off in my own world or talking to them.
This is about people, though. There's also the disconnect from the outside world. I'd have to say that my mind is my first priority, and what's going on around me is second priority. Many times, I'm completely oblivious to what's going on around me because I need to think. Even at work, I have this constant barrage of customers, handling checkouts, and dealing with coworkers. At times, I'll notice myself completely missing something I was doing because I was lost in my thoughts.
The thing with the constant contemplation, though, is it is different for each type and their cognitive processes. Take an INxJ for example. Their brain is likely filled with constant new ideas. Me, an ISTJ, though? I'm constantly thinking about how to better control my life.
But, I always thought there was something wrong me, because I have absolutely no problem spending all day alone in front of my computer. It feels like freedom. Even at school, I can so easily just put on my headphones, walk to class, listen to the teacher, rinse and repeat until I go home. I wouldn't need to interact with someone else unless I really had to. I've had to learn how to force myself. It's not hostility toward other people, although sometimes it does turn into it. I just don't NEED the focus on the outside world.
As others have said, though, I fail at coming up with answers to questions on the spot. I always chalked it up as just a lack of social experience. I've learned from the MBTI though, that it isn't always being a social outcast. I've been able to make myself tell people lately, "Just give me a little bit to think about this." Like, for instance, my sister came in my room and asked me to sell something on ebay for her, and she wanted it carried out that instant. She's an ENFJ. She could probably do that, but I couldn't. I told her to wait. I needed a little bit to think about what we needed to do and how I wanted to do it.