I've seen some situations where this can take place when data of a certain type (i.e. files, registry, ini files) have more than 10000 entries.
If you are getting this extremely slow behavior with INI or Registry data, I would recommend checking the repackaged output to see if there's anything you can exclude. The more you're able to exclude, the quicker the build process will be.
For files (when it gets stuck at 'Creating Components for Files'), there's an easier workaround--simply move the repackager project files (*.irp, *.inc, *.nir, options.ini, etc.) to another folder and build just the *.ism project file. The trick with this workaround is to have the repackager not be able to reference the installation files, since it will try to populate the *.ism with data from these files, and this can be very slow.
Hope this helps.