Jeremy Wright has compiled a list of Fortune 500 companies that are blogging. Then, Steve Rubel ups the ante and proposes that the ones who are the first movers in the blog world will fare better than the ones who don't. He even links to what would be a mutual fund for Jeremy's list.
I think Steve makes a good point. I think the blogs are a "symptom" of a much bigger asset within the company. Many of the companies that move first have a culture that enables something like a blog through the front door. The blogging won't impact the business as much as the culture that enabled it to get started.