Today I'm going to make an obvious point: the stars in a software project are the programmers (well, the architects a little bit too [;)]) no doubt about it. But the scenario is not unlike that of a music concert: the stars are the singers and musicians for sure but in order for the concert to be a success you require of far more people in many different fields, some of them totally unrelated to music.
In order for a software project to be a success you require users, domain experts, IT people, testers, etc. And above all, you require project managers, this is a job
As I said, the stars are the programmers, but just as a concert produced by musicians is doomed to be a failure, a software project made only by programmers will be a nightmare. To avoid such chaos, to have everything ready for the programmers to write their masterpiece and let the users ecstatic, we need a great project manager.
So what is it that a project manager is supposed to do? The answer is neither short nor simple, so it's great when a witty and candid book on the subject appears: The Art of Project Management, written by Scott Berkun, which got a Jolt Productivity Award in the Books General category. A recommended reading, for programmers and managers alike.