To fill in some of the mystery here...
sponsor_name must have a value due to some backend restrictions and as of 6.0 we started filling in the username when a sponsor name is not available.
If your sponsor setup is a manual email or dropdown then only sponsor_email is going to be set leaving sponsor_name to our logic.
If you are using LDAP Lookups we should be filling in both fields if it is configured right.
In all cases, when a sponsor sponsors, their name and email (assuming the email is being served to us) get set. If you are piggy-backing the LDAP lookup this will be automatic. If you are using a CPPM auth service you need to make sure email is returned.
Add register_token_confirmed to guest_users / Manage Accounts to see who has not been sponsored. You can even put "register_token_confirmed=0" into the filter box to filter just the ones needing sponsor. Or even bookmark "guest_users.php?search=register_token_confirmed=0".