Elizabeth Lawley, Director, Lab for Social Computing at Rochester Institute of Technology (New York), blogs about a conversation she had with a few colleagues, one of whom offered two reasons not to blog: A sense of obligation to keep on blogging once you've started and the need for academics to develop ideas in private, only revealing them when they are fit for review. She disagrees, pointing out that the benefits outweigh the (perceived) costs:
Yes, I feel stress about "producing" on a regular basis. Yes, I've been burned when offering ideas that weren't yet ready for prime time. But in return, I've become part of an amazing, supportive "invisible college" of colleagues, from inside and outside of academia. I've had input into ideas that have helped me shape my research agenda before I've gone too far down a blind alley, I've found people to work with on papers and conference presentations, I've found encouragement when I've been stuck on a tough problem.
This is more applicable to general academic blogging, rather than the current module blogs setup. But I feel if you're passionate about your work, you should be sharing it with the world.