Working on a test box, I tied it to the 6rolling repository. All good,
then for other testing I "yum downgraded" everything back to 6.1.

Hilarity ensued. It seems that upgrading sssd to the leading release
updates the database. Rolling back the sssd package means it can no
longer read the updated database. I wound yum deleting sssd, clearing
the database in /var/lib, then re-installing sssd and restoring all my
relevant LDAP settings before I could access my user logins again.

System users were fine, it's just the LDAP serviced accounts that were
messed up. Keep this in mind when "6.2" comes out and you upgrade.