The Pew Internet and American Life included blogs this time around. Here is what they say:
2% maintain Web diaries or Web blogs, according to respondents to this phone survey. In other phone surveys prior to this one, and one more recently fielded in early 2004, we have heard that between 2% and 7% of adult Internet users have created diaries or blogs. In this survey we found that 11% of Internet users have read the blogs or diaries of other Internet users. About a third of these blog visitors have posted material to the blog.
Blogs are like resumes/websites for individuals so I would expect the number to go up and the frequency of updates to go down.