This second release candidate focused on bug fixes and stability improvements and we hope to only require minimal changes ahead of the next release. Many, but not all, of the new features are already integrated in the official documentation on php.net.
Please not that we are aware of minor issues including that we still want to fix (though most of them have also affected PHP 5.2) and a crash bug in affecting source files with a size of exact 8k (See Bug #48934). Expect an RC3 in 2-3 weeks time, though for most users there will not be a noticeable change meaning that now is the time to start doing the final testing of PHP 5.3.0 before it gets released with any unnecessary incompatibilities with your project.
Some additional links to get started: