I generally like articles that are short and to the point. This
Wall Street Journal blog article fits the bill. It simply and precisely goes through three of the reasons many online communities built for businesses fail: 1) "They have a tendency to get seduced by bells and whistles and blow their online-community budget on technology", 2) "Most ... put a single marketing pro in charge of their sites" and 3) "Businesses say that their primary objectives are generating word-of-mouth marketing and increasing customer loyalty. Yet the metric that businesses use most often to measure success is the number of visits to the site."
Yup, that about sums it up in my mind. Well that and no one cares about their brand.