not relevent... yet
It does ring a bell, and I have tested it. however:
1) Its not finished yet, and as such isn't ready for a production environment.
2) Although I am fine with setting up a samba server (and have done it on may occasions), every other member of my staff is not. Its been surprisingly difficult to get competent Linux staff who are wiling to work in a mixed windows / Linux / Mac environment. this means there are massive training issues, and also business continuity issues should I move on.
3) Samba 4 doesn't support all the higher enterprise functions of AD... yet.
4) If your in an enterprise with multiple sites/departments. The chances are you will have windows server boxes already out there. At which point, the licensing issue is still there, even if you replace some of them with samba.
5) As much as I respect samba for its performance and rock solid abilities. Its just no where near as slick, easy to use, easy to setup, and easy to manage.
believe me, I am watching samba 4 with deep interest and can only hope it turns out as well as I am sure many of us want it to.