Northeastern University and Backbone Media recently completed a research paper that determines the reasons, conditions and factors that make a blog successful. It included interviews with twenty corporate bloggers, all of whom have been at it at least a year.
In the end, the group zeroed in on five critical factors for success: culture, transparency, time, dialogue and an entertaining writing style and personalization. If you've been studying this stuff for awhile, none of this is exactly surprising. Still, it's a good resource for people considering taking the plunge.
