What is the difference between versions? Does 1.5.7 include new Example Sketches? Support for more Arduino boards?
Mostly, 1.5.x supports more boards; specifically, the non-AVR boards like the Due. In fact, it implements new infrastructure that allows any number of platforms to be supported or added to the IDE.
So how does this effect the libraries? I notice some external non official libraries have both versions available. Is this necessary?