The answer might surprise you. It did me. At first.
When looking at Twitter, you'd expect most of the folks who would be on Twitter would be extroverts - who gain energy by socializing and interacting with other people.
You'd also think SP's or the Spontaneous type would be naturally drawn to Twitter. These past paced, sometimes impatient folks would love the 140 character or less communication style. Tweeting seems like a Spontaneous activity.
So, a good guess for which personality types love twitter would be extroverted spontaneous folks (ESP's).
(obnoxious horn blow) Wrong!
According to a recent article on the mbti blog, it seems the personality types who love Twitter are NF's (Humanistics) and NT's (Competitives) AND Introverts.
In my unscientific survey of the MBTI preferences of English speaking Twitterers (286 as of this post), here's what I found....INFP's rule Twitter!!! Contrary to their representation in the general population, INFP's and INTJ's are heavily represented in the Twitter community. Again, contrary to the general population, ISTJ, ESFJ, and ISFJ, and ESFP's are all under-represented in the Twitter Community.
At first, this surprised me. But then, being a good little INFP, I sat down by myself and thought about it for a while. And it actually started to make sense.