The OpenGroup has registered Apple's MacOS X as an entity entitled to bear the UNIX trademark. This is of course a big step for MacOS X, which is now officially an UNIX operating system.
At the same time, however, this invalidates the claim that MacOS X is a BSD operating system. This claim, voiced loudly by MacOS X users confronted with BSD operating system users, has always been technically wrong, since MacOS X is not derived from or compatible to BSD operating systems. Nor are its drivers in any way. Normally, BSD drivers can be made to work on all BSD operating systems using only a small amount of #ifdef work.
MacOS X is a reimplementation of a kernel and userland which provides, amongst other things, a BSD compatible API to userland programs. It also ships with some tools that also exist under BSD. This, however, doesn't make it a BSD operating system.
The new legal argument also speaks against MacOS X being a BSD operating system: for historical reasons, the BSD operating systems cannot obtain the UNIX trademark, even though they all pass the UNIX certification requirements. The amicable arrangement in 1993 in the case of AT&T versus the University of California, Berkeley, clearly states this. Thus, legally, a BSD operating system can never be an UNIX operating system. Thus, if MacOS X is UNIX, it cannot be BSD.
Thanks a lot to Apple for making this clear.