Gosh, it is such a shame to defile a great OS with a bad name (cihost)...
I run OS X on all my computers at home and the office, and LOVE IT.
However, would I host websites on an XServe... eh, not at this point. It's not that there is necessarily anything WRONG with it, I just haven't seen resounding proof that the benefits would be so outstanding as to warrant the effort. Frankly I like my RedHat stuff just fine.
Apple's OS X Server OS and GUI sound sexy, but I haven't had a chance to read or play to give it a yay or nay.
Absolutely love my OS X desktops and laptops though. The OS is FreeBSD based and it is absolutely a gorgeous thing.