According to a recent Business Week article, municipal debt backed within Puerto Rico has lost almost 20% this year to date. This is triple the losses experienced by the overall municipal bond market in the U.S. Further bond downgrades could have significant and lasting effects on the Island and on investors in Puerto Rican based municipal bonds.
http://www.businessweek.com/news/2013-09-09/puerto-rico-yield-penalty-doubles-as-island-s-economy-shrinks.