Here are a couple of links to articles discussing how academic blogging can negatively affect a person's job prospects:

http://chronicle.com/jobs/2005/07/2005070801c.htm

http://arstechnica.com/news.ars/post/20050711-5080.html

The former is from the Chronicle of Higher Education while the latter is a personal narrative from Hannibal, a well-known technology commentator on Ars Technica. Perhaps most interesting is Hannibal's objective statement that graduate students simply shouldn't blog under their own names, nor should they respond to controversial forums. The benefits do not outweigh the possible consequences. (I wonder how much jeopardy I am putting myself in through this comment.)

I think what these articles reiterate is something that should be obvious to anyone in academia: you function through a persona. That persona must be maintained and nurtured like a backyard vegetable garden in sunny Lafayette, Indiana. As always, we must be judicious in the presence we construct. The technological possibilities for information exchange have outstripped academia's capacity or desire to absorb them. This isn't merely a case of "don't put anything online you wouldn't want hiring panels to read," but rather, construct your online academic persona in such a way that what is associated with it is productive and targetted. Demosthenes mentioned something about delivery...

(In the interest of—ahem—full disclosure, I should point out that although I do occasionally comment to blogs like this one, I have never been much of blog participant due to its almost overwhelming noise to signal ratio. I feel that although blogs can be productively deployed in some scenarios, the blog is being over-applied and will suffer an inevitable backlash [which these articles may suggest]. As such, I do not publish a blog, although I do post current works in progress and some biographical information on my homepage.