Without giving away too much, we launched some internal blogs at work. We started with two VP's and we've even had our first flame war. Much fun indeed.
I believe that once people realize that, "wow, I have a boss who posts this stuff online without fear, I can comment and tell them what I think, without fear.", you get a rather free-flow of information and you build an audience. It's far from the typical company publishing something about promotions or a tweaked press release. When you write something unique, people want to keep coming back for more.
The flame war was interesting, we went from 1 to 5 comments on posts to one post with about 50+ comments. We had all levels going back and forth....managers, techies, claims processors, every level of the company...maybe sans VPs arguing about a couple of touchy issues. With new-found "freedom", civility can sometimes take a backseat.