>>50
The author of this HFS metadata test suite (http://www.n8gray.org/blog/2007/04/27/introducing-backup-bouncer/) tested against xar svn (fix later released in xar 1.5.1) and found it to handle all known HFS metadata correctly. You can simply use this suite to generate sample archives and verify how much metadata is preserved. It would be interesting to see if the Unarchiver's zip, tar, cpio and pax implementations are capable of restoring whatever metadata that's actually preserved by the archiving program.