OS X is Unix
Macworld posted an article taking a look at Mac OS X from a Unix perspective.
Apple has taken an enormous risk by abandoning the fifteen years of development it invested in the original Mac operating system, but judging from the Mac OS X beta, that gamble has paid off. The Macintosh can now run with the big boys, supporting the attractive and elegant interface the machine has always offered with a rock-solid Unix foundation. Literally millions of lines of code, comprising some of the most powerful server-side applications ever written, are suddenly Mac-compatible. The tools that were used to write those applications, and the operating system features they rely on, are also available.
And so the revolution begins...