Over at Living the Scientific Life, GrrlScientist has a nice post summarizing a recent article by David Secko in The Scientist (don't bother with the link, it requires subscription!) on The Power of the Blog. She says:
Secko's article is a general synopsis of the value of blogs to scientists, and to biotech and pharmaceutical companies. In this essay, I condense Secko's piece for you, adding considerable commentary of my own, and then conclude by offering a few of my own opinions regarding the value of blogs to science.
Do read her post. Several others have commented on this post; in particular, Chad Orzel and P.Z. Myers. Myers' post also linked to an earlier debate about academic contributions of blogging, and its follow-up.