Reading the e-Week Article "It's the Directory, Stupid", I got thinking.
From a commercial scale perspective, Active Directory has done quite well. The author mentions that RedHat/Fedora has not really pushed the Directory Server into the enterprise. I am not going to comment on that but would like to say that the FreeIPA (http://www.freeipa.org) initiative is certainly an excellent platform for enterprise customers to handle Identity, Policy and Audit requirements in an heterogeneous infrastructure. The proponents of the FreeIPA program told me that there are customers who have deployed Active Directory based infrastructure would like Linux to inter operate with it.
Coming over to efforts on Java based Open Source Directory Servers, the prominent DS at the moment with rich feature set is the Apache Directory Server. On the other hand, the Sun Open Source Java Directory Server, OpenDS, has had some bumps along the road recently.
Multiple SMB infrastructure may be running on OpenLDAP, but I have to agree that when it comes to scalability at the enterprise level, it has fallen short (as mentioned in the eWeek article).