Here is Virginia Postrel (NYT registration required), telling us that TV shows need dispersed word of mouth to succeed:
Another factor did, however, predict whether a show’s audience would build over time: dispersion, or “entropy.” This technical measure essentially picks up how widespread the discussion is. Are comments concentrated in a few specialized groups, or does the show interest people in many different groups? Word of mouth spreads more quickly when it begins in different places or among people with different interests.
“It’s not enough to say that we got 10 mentions for our product or 10 people are talking about my research,” Professor Godes says. “To understand the impact that word of mouth is going to have, you have to understand how different those 10 people are.”
To take an academic example, he says: “Ten people sitting at Harvard talking about my research all talk to each other. I’d rather have one person at Harvard, one person at M.I.T. and one person at U.C.L.A. talking about my research. That’s really how the word will spread.”
Here is an interview with the original authors of the research. Here is a link to the working paper. The authors should be pleased to know that their hypothesis is making its way around the blogosphere.