I tested restoring a Drupal website by having backuppc generate a tar file, uploading the file to the server and then extracting the tar file to the new Drupal directory structure.  A large number of files were not restored because a number of Drupal sub-directories are read-only.  Errors included 'Cannot open: Permission denied' and 'Cannot open: No such file or directory'.  

I found a reference to the '--delay-directory-restore' option at http://www.gnu.org/software/tar/manual/tar.html#SEC77 that solved this problem.