I am experimenting with OpenLDAP now too.
I have set up an address book for my office. Users can access contact info. such as names, addresses, telephone numbers, email addresses, etc. straight from Outlook Express or Eudora. I suspect other packages can be used as well, but I have only tried it with these two.
We have one big list of contacts. This info. is not confidential so we have not set any authentication requirements. The only restriction is that users can read but not update the database.
Some basic info. re: setting access controls is available in the OpenLDAP 2.1 Administrator's Guide. http://www.openldap.org/doc/admin/
Go to the section on Access Control.
What do you want to do with LDAP? I have read about using it for Samba authentication, mail routing, directory services...