The idea behind Paid Learning is making it possible for learners to convert newly acquired knowledge into cash, right away.
For example, in the area of Free Software, many tasks are composed of small sub tasks that people may be willing to pay for and that don't require an expert to do. Dividing tasks and directing them to the right people, however, is certainly not easy. That's problably the reason why Paid Learning is not available today, at least not on a large scale. What lies ahead of us is the development of suitable technology and of suitable consulting models.
For further information, see the page on education in the Tag Trade wiki for an introduction concerning paid learning. Naturally, Tag Trade is not the only system that's suitable as a backend for paid learning.