Take Kiva for example; I have been donating, loaning, and re-loaning my donations for about three years now. The organization is rather complex in itself, not taking into account the lives of those farmers, seamstresses, plumbers, computer technicians, that rely on their loans and support to meet their basic needs and support their business. My guess is that Muhammad Yunus really didn't consider the true possibility and probability that his simple concept could make such a sincere, universal impact.
But, micro lending does not go with out criticism and such. Many have tested this concept and incorporated it into their for-profit companies. Hearing about these companies, Yunus simply replied that he "never imagined that one day micro [lending] would give rise to its own breed of loan sharks." More than criticism from others with the economy field, Yunus deals with this new problem of "loan sharks."
Yunus was awarded the Nobel Peace Prize in 2006 as the first Bangladeshi to be given this honor. From there, he announced that he would be starting a line of food that is low cost, high nutrition and high availability for impoverished children. Along with that, he decided to found eye hospitals around Bangladesh for those who cannot afford their own doctor.