The folks at Innovation Zen make a good case for this:
“Imagine you are a prospective employer, and you can compare two identical candidates. The first candidate has simply handed you a 2 page resume + 1 page cover letter. The second candidate has done the same, but they have also included a link to their blog. Now, further imagine that although the blog gives a more detailed picture, it does not change your opinion of the second candidate. Which candidate would you choose? My guess is that you would choose the blogger simply because they are a known quantity.”
I like the idea that we are our own “brand” and a blog is THE best tool for promoting same.