How Unix-like is MacOS X?

prospective_user asks: "I am a heavy user of Unix, spend most of my time running Linux and am considering getting myself an iBook, after seeing a considerable amount of exposure Macs/Apple have in both Slashdot and the O'Reilly Network. Given that MacOS X is based on FreeBSD/Mach, I suppose that the usual Unix libraries and environments (like ncurses and tcl/tk) are available in MacOS X (which I hope is true, for text-based applications). In fact, I'm concerned about the Unix side of MacOS X and also plan on running Debian/PPC on it, but I plan to primarily use MacOS X. So, before having an (uncertain) investment in a new platform, it would be reasonable to have a bit more of background on it and thus, the questions: how well does MacOS X support traditional Unix applications? For instance, how do the following applications run under MacOS X (which I use the most): teTeX, GNU Emacs, mutt and fetchmail?" Note that the submittor isn't asking if OSX is or is not a Unix; we've fielded that question already. No, the question here is where does OSX differ from the other unicies.

"Also regarding the investment in a new platform and coming from the x86 world, I'm a bit interested about the PowerPC performance in comparison to what I could get with a x86 notebook. I've read some articles and pages that suggest that PowerPCs may not be fast (or, in fact, may be quite slower than their x86 counterparts):

Some of the sources I've read are: these pages, from D. J. Bernsteins's website, and this article on processor performance from the GMP website.

Also, as some later questions, can the portable Macs be plugged to non-mac monitors? And does MacOS X feature a packet filter like Linux or other BSDs do?

Any comments and experiences with these machines are welcome. Thanks."