Great article in BusinessWeek by Spencer E. Ante and Catherine Holahan about how the promise of an advertising bonanza on social networks is not paying out.

They point out 1. the boom of millions of new users is slowing down 2. the average amount of time people actually spend on sites is dropping 3. Worse yet, users appear to be increasingly less receptive to ads.

A great help in understanding the challenges around monetizing social media.