Forrester analyst, and blogger, Charlene Li announced Forrester's latest look at so-called "corporate blogging" (see post here). I haven't read the full report, but Charlene's post, and the Excel model she linked to (here), provide significant detail on the model. The full report is available to Forrester clients free of charge or to anyone else for $379 here (see also, Charlene's powerpoint presentation that accompanied her December webcast on the ROI of blogging here).

I'm sure there will be plenty of debate about the assumptions that went into the model, but here's the bottom line for one of the highest profile corporate blogs, General Motors Fastlane (see screenshot below; Forrester case study on Fastlane available for $279 here).

Blog benefits (2006): $410,000
  - PR value (articles) $215,000
  - Product feedback value (virtual focus group) $180,000
  - Word of mouth/awareness value $15,000

Blog costs (2006): $255,000
  - Producing content (mostly exec time) $155,000
  - Brand monitoring service $50,000
  - Blogging platform $25,000
  - Review & direction $21,000
  - IT support $3,000

Net value to GM (2006): $155,000
ROI: 69%

Much of the blog's value stems from the product feedback gathered and press articles written about the blog or what was mentioned in the blog's posts and/or comments. The estimated value of the word-of-mouth generated is minimal, just $15,000.