Mark Potts, in his Recovering Journalist blog, posts an economic reality check on the musings in recent weeks about introducing micropayments or re-erecting firewalls for online content.
In his calculation, it just doesn't make sense (no pun intended). The revenue would be small and the advertising losses big. In his view, the best next step is to search for more ad revenue --- those gains are much more substantial than the gains from subscribers, and while the long-term effect might be more revenue, the meantime effect is a real loss in traffic.