Overall, bloggers are a highly educated and affluent group. Nearly half of all bloggers we surveyed have earned a graduate degree, and the majority have a household income of $75,000 per year or higher. As blogging is now firmly a part of the mainstream, we see that the average blogger has three or more blogs and has been blogging for two or more years. We are also noticing an ever-increasing overlap between blogging and mainstream media.
So who are the bloggers? Let's delve into the demographics:
• Two-thirds are male 
• 60% are 18-44
• The majority are more affluent and educated than the general population
    ◦ 75% have college degrees
    ◦ 40% have graduate degrees    ◦ One in three has an annual household income of $75K+
    ◦ One in four has an annual household income of $100K+
    ◦ Professional and self-employed bloggers are more affluent: nearly half have an annual household income of $75,000 and one third topped the $100,000 level
• More than half are married• More than half are parents
• Half are employed full time, however ¾ of professional bloggers are employed full time.

Source:- http://technorati.com/blogging/article/day-1-who-are-the-bloggers1/