The networks will employ entrance polls from Edison Research (you can't exit poll a caucus) tonight in Iowa. As Todd Beeton notes, this provides a strange dynamic in that we will have entrance polling data analyzed on television BEFORE the caucuses are completed. Stoller opines, correctly in my view, that:

I'm starting to think that the entrance poll will determine the media narrative after Iowa, not the final caucus results. If someone wins the entrance poll, but loses after second-choices are allocated, both the campaign and the media will point that out in pretty much every write-up of the caucuses.

But what of the things the Media will talk about before the caucus is over? Turnout will be the main thing. I believe they will talk about what percentage of the caucus goers are Democrats, Independents and Republicans. If you have been reading me, you know that I believe that Obama's win will depend on historic Independent and Republican participation in these caucuses. We will know if that happened based on these entrance polls. In essence, I believe we will know what will happen based on that result, which we will know BEFORE the caucuses are even finished.