Inside the Secret World of the Data Crunchers Who Helped Obama Win
I think polling on such a detailed level is fundamentally changing the democratic process. In the past, politicians had to be leaders - present a vision that was quite possibly unpopular to start with, and persuade people to come around to it. (See e.g. JFK and the space program.) Nowadays they're becoming expert hagglers: keep this mini-group barely content, say exactly the right nice things to the other, ignore a third altogether because they're 10% over in enemy territory. I don't know where this is leading to, but it's definitely a big change.