Great post from Stephen Downes on his “Half and hour” blog titled The form of informal in which he further explores the difference between formal and informal learning. Summed up well in this statement I feel:

What makes informal learning different from formal learning is not that it is formless, but rather, it that it is conducted outside the domain of the formal education infrastructure, with the associated and not trivial implication that it is managed by the learner, and not the professor or institution.