I recently finished Flat Earth News by Nick Davies. A book well worth reading, in my humble opinion (and reviewed here). The associated website lets you read some of the sections from the book. The book's release was strange, in that the British print-media tried to ignore its existence - simply because they were the ones on the receiving end. It was only through Private Eye that I even knew it existed.
It was the final chapter I personally found most depressing. It was about how the Daily Mail operates. The gist of it is that the Daily Mail knows exactly what its readers want to read, so they ignore positive stories about, for example, black people (regular English black people, not *even* 'asylum seekers') and seize on the negative. They pander to the ingrained prejudices of little englanders to maximise revenue.
Now I had always assumed such behaviour was borne out of institutionalised racism and xenophobia, and that the likes of the Daily Mail led ordinary folk to have bigoted opinions. Instead it turns out that the readers are already bigots, xenophobes and racists and they read the Daily Mail simply to have their prejudices reinforced. If the Daily Mail didn't tell them what they wanted to hear they would turn elsewhere. Therefore, it would appear, that paper, despite massive sales, not only does not have the power to change opinions, it doesn't even have the power to tell a rounded story for fear of pissing off its readers. My heart sank reading it.