“Tiger also represents a milestone in Mac OS X’s development process. Apple has promised developers that there will be “no API disruption for the foreseeable future.” Starting with Tiger, Apple will add new APIs to Mac OS X, but will not change any existing APIs in an incompatible way. This has not been the case during the first four years of Mac OS X’s development, and Mac developers have often had to scramble to keep their applications running after each new major release.”
This is a GREAT in-depth review that any Mac user (and not) will want to read. Check it out at Ars Technica.