I used it, at a client site. Why? Based on legacy. It was replaced as QUICKLY as possiable due to technical shortfalls in the OS. This was on a 1U OSX Server power architechture. 10.4-10.5 era (while I was subjected to it's horror).
What on earth possessed apple to supply a system with 3 drives, while at the same time haivng no support for a RAID5 in it's software RAID stack? I mean really, you say RAID, you say 3 drives, you think RAID5. But no. Do not try before accepting the usual apple "pay for features" attitude and purchasing a flimsy hardware device which is a supposed RAID controller. Oh ya, and as the earlier posts have documented, Apple cant figure out ZFS, that project's dead, just like OpenDarwin, just like any other externally facing Apple corporate initiative.
The UI has the usual issue with any X based applications, the inveritable desyncronization between daemon's config files and the UI's interpretation of what the settings are.
Apple's gone through all the trouble of de-standardizing as much as possiable as part of their market retention stratagy, luckially several replacement OS's work fine on their hardware (well, not really theirs any more), so it's a MASSIVE pain to manually fix any config settings or attempt even a modestly realistic deployment scenerio. And the SMB works like garbage, their smb.conf almost always configures oplocks that render shared files locked and frequently in need of an administrative finger to bounce the smbd.
It would be too easy to go on with significant shortfalls and other excessivly frustration points with their software. I beg any crapple whackintosh fan-boy put down the coolaid for a second and take an honest look at their platform (sorry but I spent a few too many hours managing what messes I've been handed as a result of apple's marketing department's over-active imagination).