Before I joined my employer we were already using ldap for storing users and customer data. The reason to pick ldap was that it matched with active directory.
It seems we can no longer scale on ldap. The main reasons for us to move away from ldap:
1) Index creation requires restarting ldap. WTF. this is a big no no for any decent size company because this makes ldap a Single point of failure.
2) Schema changes requires ldap restart.
3) No a very big community support like we have for mysql and other relational databases.
4) Scaling developers is tough, for most people ldap is alien technology.
5) Loading 5K users in ldap took 2 hours as after a point like 5-10M users in a ldap the insert performance just sucks.
we recently migrated some customer from ldap2mysql and all above 5 points are solved by moving to mysql. Even the performance of insert rocks in mysql.