In summary, here's what the statistics indicate about the correlation between personality traits and IQ:
Other personality traits being the same, an iNtuitive person (one who grasps patterns and seeks possibilities) is 27 times more likely to have a high IQ than a Sensing person (one who focuses on sensory details and the here-and-now).
Again, other traits being the same, an Introverted person is 8 times more likely to have a high IQ than one who is Extraverted; a Thinking (logic-oriented) person is 2.5 times more likely to have a high IQ than a Feeling (people-oriented) person; and a Judging person (one who seeks closure) is about twice as likely to have a high IQ than a Perceiving person (one who likes to keep his options open).
Moreover, if you encounter an INTJ (Introverted, iNtuitive, Thinking, Judging), there is a 37% probability that his IQ places him in the top 2 percent of the population. The probability is 20% for an INTP, 15% for an INFJ, and 8% for an INFP. These four types account for 66% of the high-IQ population but only 6% of the total population.
* August 26, 2007: I apologize for not having documented the source of the statistics that I cite here. I dimly recall finding them on or via the website of Mensa USA, but I am not certain of that. And I can no longer find the source by searching the web. I did transcribe the statistics to a spreadsheet, which I still have. So, the numbers are real, even if their source is now lost to me.