I just posted version 0.7 of the String lib, which is basically the bug fix Mikal Hart posted. Sorry for the long delay. String is not part of the core, so it's always been a side project for me, and one I only get to once in a blue moon. The memory bug,at least, should now be gone. Thanks Mikal.
This is an interim version. Hernando Barragan made some nice API changes for a Wiring version, but they change the core libraries a bit, and have not yet been ported over fully. There are also some changes I want to make, because there's some nomenclature and behavior I'm not happy with. Xiaoyang Feng is working on this. The major issue he's working on is to make the library portable without need to modify the core, and to reduce memory usage somewhat. If anyone wants to jump in on this task, mail me.