There is a new build available, Wenatchee 2009-06-24, with many new features, enhancements, and bug fixes with the main focus on new 2-d functionality.
Everyone is invited to download and use the OS X version of Rhino while it is in development.
Most of the core functionality has been ported from Windows and is very stable. There is still much to do to port the rest of the functionality and refine the interface. We don't expect the first commercial release to be ready for at least a year.
Don't worry if the build you are using is going to expire. New versions will be available every few weeks. There will be a newer one available before the expiration date.