[Samba] OT: Why are so many using Samba to authenticate as PDC??

[marvc]

I need to get some feedback on some good reasons for incorporating Samba
into a corporate environment that runs mostly Microsoft, but also Sun,
and some linux systems. Can anyone here that have used Samba for more
than a few months elaborate on some of their reasons for choosing to use
Samba? Advantages and disadvantages are also welcomed. 

Many thanks in adcance.