Jon Udell references articles from Andrew Odlyzko and Sˇbastien Paquet in an article about peer review, academic research, and blogging. Being a once and future (I hope) academic, I have given some thought to this question myself.
I think Sˇbastien misses a very important point on why more academics don't blog as part of their research efforts: tenure and promotion. Tenure and promotion depend on one thing (protestations about teaching aside): published papers in established research journals. In this false economy, every other activity, including blogging, is in constant competition for the resources that could be applied to publishing in peer reviewed publications of note.
The problem that this poses, is that this system is not necessarily the best one for measuring the importance or impact of a scholar's work---its simply the one that is trusted the most. This is especially true in the field of information technology. By the time something makes it into a printed journal, the research is almost certainly 3-4 years old. So, right now you could expect the first papers based on research done in 1998. That simply isn't fast enough in the fast paced world of IT. When you want to find out what's innovative in computing, you don't turn to the Journal of the ACM, you open up InfoWeek or some similar trade magazine.
Will this change? I agree with Andrew that its changing already, albeit slowly. There are other indications of a researchers innovation and impact, like the number of readers of a blog or work with a company. The problem is that its hard to count and comes up against a measurement system that is trusted, for good or bad, by nearly everyone. Academics will take their own sweet time, but eventually come to grips with new modes of communication and how to measure it. Whether these other indications ever play a part in tenure and promotion decisions remains to be seen.