Chris Anderson’s Counterintuitive Rules For Charging For Media Online
techcrunch.com
techcrunch.com
It seems to me that the market will be significantly more subtle than this. Popular items will be the easiest to charge for (think about the excitement about the Harry Potter books) but they could also be used to promote stuff (give away music but then make money from concerts).
By his logic, niche items can be free and most likely will be free. In my view, you will be able to charge for niche items that are extremely popular relative that niche (consider how expensive general math books are) or for content that is markedly higher quality than the free stuff (think premium software, i.e. Oracle vs mysql).
Walt Mossberg of the WSJ is really popular in tech so it's not very "long tail" but he has the exclusivity, insight and trust worth paying for.