We have had the same problem of the string shredding with our shades in our 04. It has been the shade next to the lounge chair and the one behind the couch. The first time we had The Dirty Blind Man come take the shade off and fix the string. He said then that he had seen various manufactuers change the plastic gromet the string goes through in on the metal handle. This plastic gromet does not cover the sharp metal edge and shreads the string. He worked on it and got the gromet above the metal edge and restrung the shade.
The second time we just called The Dirty Blind Man and he sent us a kit to repair it our selves. Mike needed help getting the shade back up, it was the big one behind the couch but did it.
If anyone is interested The Dirty Blind Man has a web site http://www.dirtyblindman.com