- reliable : besides the 2nd HD giving SMART errors and that I had preventively changed, I never had one hardware problem in over 3 years. It's on 24/7 and on UPS. I have a second one without UPS, also working like a charm.
- small : whenever you need a server, it will fit.
- green : it won't suck too much power, so it won't overheat. I live in a tropical climate- this matters to me.
- versatile : it can be reconverted into a small desktop when you no longer need it.
- standardized : you don't have to worry about the video card or the revision of whatever internal piece changing between batches. If you compile your own linux kernels, that's a godsend.
- easy to find : you need one in a hurry? There are applestores everywhere. now try and get me a dell server in the next hour.
- osx already installed : sure Linux might be better in many cases, but my time is not free. OSX total configuration time tops 20 minutes, including plugging cables.
- quick to configure : if you just need something for php+psql, download osx server package and you're ready to go (That's included in my 20 minutes estimate). It's sucking less than the previous versions (I hated snow leopard server). If you are not in a big hurry, I recommend instead to install your own utilities.
In both cases you can keep .dmg, which is useful in some work environments where for security reasons there is no internet connection.
Oh and here is a reason why I love rudix - prepackaged GNU utilities, with everything included.
No I do not want to recompile stuff. No I do not want to even think about tracking dependancies! If I need say mc, I want a .dmg which contains the whole thing and the libs, and that I can install on another machine immediately without worrying about glib or stuff.
TLDR; the mac mini is great. OSX Server "acceptable", but most of it can be replaced by rudix.
Sure you may be better served by a custom built machine, or a cloud service, but when you want something working ASAP on an intranet, I haven't found anything better yet.
I'm not even talking about the sweet no-questions apple warranty, or the rescue procedure standardization (alt key : will boot on CD or USB) common to all apple hardware. I don't want to remember if F1 or F10 or F12 will get me in the bios, or where I will have to click to let me boot from usb.
I buy mac minis because it's the best hardware I've found for my needs (and I say that while trying some hackintoshes time to time!)
If you haven't tried one yet, it is worth experimenting with.
BTW on http://store.apple.com/us/configure/MD389LL I see the 16Gb RAM upgrade is getting "more affordable", but I really would like to get a mini with 32 or 64 gigs.
EDIT: I know that RedHat, Debian, etc installation can be automated. If you have thousands of identical machines using known-to-be-supported hardware, and highly specific needs requiring a gazillion of .debs it's great (+)
But let's say it's 7pm and you need just one machine with apache to serve a php website on the intranet. Do you want to automate an installation and tweak it, or just take a box where a Unix is already installed, along with vi, apache, and the basic tools you need? Some minor configuration file edits will make that box production ready in a matter of minutes. (And BTW OSX software installation can be automated as well)
+ : automated installs do not fully remove hardware variation issues or make sure the drivers work. The best part of apple hardware is that it generally evolves very slowly - your kernel bins, modules, etc. will usually require more tweaking on 5 dells of the same model than on 20 different imacs (!)
In the ends, it's all about costs, and return to scale.
If you have thousands of linux boxes, it's a good idea to use cheaper hardware (and buy spares!) along with install automatization : high fixed cost, low marginal costs.
For lower volumes, a different solution means I have to spend far less time on it, which lets me concentrate on the real work.