This is hearsay but what I understood is that there is no suitable large scale alternative for MS Active Directory and that it doesn't play well with Linux setups as it does with Windows. I didn't see this mentioned, so I thought I would, maybe someone with more experience in this kind of management can chime in.
from personal experience it is a bit harder (or was, last time I checked) to manage file permissions vs Windows. As far as AD, Linux has had LDAP (which AD is based on) for quite a while.
