This is more evolutionary than revolutionary as far as microfinance is considered (for reasons below), and that's a good thing because there is no need to reinvent the wheel.
1) Repayment rates over 90% are not uncommon among existing microfinance lenders. Grameen Bank's rate is 97.6% - http://www.grameen-info.org/index.php?option=com_content&tas...)
2) Unlike mortgage providers who have a wealth of credit information for applicants, microfinance initiatives do not have this. Traditionally this has been solved by lending to groups and if any one person in the group defaults, the entire group is barred from future payments. This enables the MF lender to harness information held about individuals to screen non-creditworthy individuals.
It's a clever mechanism and I'd like to know more about how Zidisha uses facebook data to similar effect.