That is an interesting question, an answer to which was attempted in this paper:

Who blogs? Personality predictors of blogging:

The Big Five personality inventory measures personality based on five key traits: neuroticism, extraversion, agreeableness, openness to experience, and conscientiousness [Costa, P. T., Jr., & McCrae, R. R. (1992). Normal personality assessment in clinical practice: The NEO Personality Inventory. Psychological Assessment 4, 5-13]. There is a growing body of evidence indicating that individual differences on the Big Five factors are associated with different types of Internet usage [Amichai-Hamburger, Y., & Ben-Artzi, E. (2003). Loneliness and Internet use. Computers in Human Behavior 19, 71-80; Hamburger, Y. A., & Ben-Artzi, E. (2000). Relationship between extraversion and neuroticism and the different uses of the Internet. Computers in Human Behavior 16, 441-449]. Two studies sought to extend this research to a relatively new online format for expression: blogging. Specifically, we examined whether the different Big Five traits predicted blogging. The results of two studies indicate that people who are high in openness to new experience and high in neuroticism are likely to be bloggers. Additionally, the neuroticism relationship was moderated by gender indicating that women who are high in neuroticism are more likely to be bloggers as compared to those low in neuroticism whereas there was no difference for men. These results indicate that personality factors impact the likelihood of being a blogger and have implications for understanding who blogs.

You can also read a brief summary here: Dear World: What kind of a person blogs?

Around 20 per cent of the students blogged, mostly about their personal experiences. Among female students only, those who scored highly on neuroticism (i.e. anxious, insecure characters) were more likely to blog. This is consistent with work on internet usage that also found an association with neurotic personality types, but only among women. The researchers surmised that nervous women may blog to “assuage loneliness or in an attempt to reach out and form social connections with others.”

Among both men and women, those who were more open to experience were also more likely to blog – perhaps unsurprisingly given that blogging is a relatively new phenomenon and given that this personality dimension is associated with creativity.

The researchers cautioned their findings may only be applicable to college students in America and called on future research to look at why people blog. “It is important for social scientists to continue to examine this phenomenon to fully understand its affects on psychological processes that differentiate it from other similar forms of self-expression,” they said.

You can take your own peronality test used in this study here (my results are under the fold).

Of course, as they warn, this is not a representative sample. These are very young people, mainly writing personal journals. If the sample was taken at a typical BloggerCon, where most people are 30 or older writing about technology or politics, they would probably get different results. If they polled academic bloggers, including science bloggers, they would probably find something else again. But it’s a good start with interesting results.

I’m a O80-C13-E93-A94-N5 Big Five!!

Openness to Experience/Intellect
High scorers tend to be original, creative, curious, complex; Low scorers tend to be conventional, down to earth, narrow interests, uncreative.
You enjoy having novel experiences and seeing things in new ways. (Your percentile: 80)

Conscientiousness
High scorers tend to be reliable, well-organized, self-disciplined, careful; Low scorers tend to be disorganized, undependable, negligent.
You probably have a messy desk! (Your percentile: 13)

Extraversion
High scorers tend to be sociable, friendly, fun loving, talkative; Low scorers tend to be introverted, reserved, inhibited, quiet.
You are extremely outgoing, social, and energetic. (Your percentile: 93)

Agreeableness
High scorers tend to be good natured, sympathetic, forgiving, courteous; Low scorers tend to be critical, rude, harsh, callous.
You are good-natured, courteous, and supportive. (Your percentile: 94)

Neuroticism
High scorers tend to be nervous, high-strung, insecure, worrying; Low scorers tend to be calm, relaxed, secure, hardy.
You probably remain calm, even in tense situations. (Your percentile: 5)