In every larger company I worked for they used LDAP as a way to access the central repository of user information, but very few have taken efforts to extend the schema to include objectClasses that aren't derived from inetOrgPerson.
Microsoft's Active Directory makes extensive schema extensions but very few commercial products leverage the capabilities of LDAP.
Is it because most LDAP developers don't know how to model beyond users? Find value in it but just haven't thought deeply about it? Have tried it and ran into performance problems? Something else?l