Devoted to branding and building and protecting brands

At latest count, less than five percent of the Fortune 500 publish blogs open to the public. And they're the tech companies.  I still don't know if this is good or bad, or how it's progressed.  Steve Rubell probably knows.  Ask him.  Point is, a lot of hoo-ha has been made about how blogs are destined to become Corporate PR 2.0 -- and that in less than five years, every F500 outfit will have one.  And they might...IFthey can see a return on investment.  Odds are long this will happen by then.   At this moment, ad agencies, PR firms, cult-of-personality consultancies (Tom Peters, et. al.) and anybody whose thinking and speaking  is their stock in trade utlilize blogs the way musicians utilize club dates.  They're central to the sell.  But what about  Andarko Petroleum, Navistar, Phelps-Dodge, and Suntrust Banks? How would/could/should a corporate blog enhance their brands? How would they measure ROI?  What's in it for them?