"I just want a simple, unmodded Minecraft server!!"
If all you want is a simple minecraft setup, no speed optimizations, no interface, no backup... you can. Whether you're Windows or Linux, you can get the files and instructions from http://minecraft.net/download.jsp directly. MineOS might just complicate your life if you're not looking for much else than some single download that starts a server.
"I'm using Windows/Linux. I play on the operating system I want to host a server with."
This is not an ideal setup. Servers are meant to serve, desktops are meant to play. There's a lot of bloat in OSes that make this setup quite slow, though easy to configure. If this is your situation, you should also just get the files and instructions from http://minecraft.net/download.jsp.
"I have a Windows/Linux server machine. It's meant to do more than just serve Minecraft."
No problem! Decide first what else your server should do than serve Minecraft. Host a website/forum? Host a teamspeak server? These are things that are easily done atop an existing MineOS CRUX server. Of course, if you have an existing server doing these functions, MineOS will happily run within a virtualized environment, such as VirtualBox or VMWare server--with MineOS' small footprint and the inherent protection offered by virtualization, this is an easy configuration to get off the ground!
"I have a Linux server machine. If all it does is serve Minecraft, I'm happy."
Many admins have old machines (or new!) which are sitting around and would be perfect for no other purposes than hosting a Minecraft server--and getting the most of the hardware. MineOS SHINES here.
Burn a CD and have your computer boot directly from the CD. These steps walk you through formatting/partitioning your hard drive and installing MineOS to the hard drive. When through, you can rest assured you are maximizing that hardware's potential.
"I want to see what RAMDISK Minecraft servers are all about."
Ramdisks are an advanced configuration made easy thanks to Linux's simplicity. With MineOS, you can turn on or off a ramdisk at will. If its a simple curiosity, install MineOS on VirtualBox and truly see what makes Minecraft servers fly.
"I use Ubuntu Server. Why would I use some distro managed by a single individual?"
If you use Ubuntu Server, either because you heard about its stability, community, or flexibility--whether you are a novice or a guru--there is still much you can take away from MineOS CRUX. If you consider yourself Linux-competent, know how to set up ramdisks, rdiff-backups, are using McMyAdmin--then by all means, continue on! MineOS offers the ease to the novices and it offers the time-saving to the gurus. I've done my best to be thorough in simplifying Linux while compromising none of its capabilities. If you fancy yourself good enough to strip down Ubuntu Server to 25MB ram footprint, create your own management interface or make ramdisks and cronjobs a click-easy process, you are part of the few to whom I need not recommend MineOS to any further.
This should cover most use cases of MineOS. If you have any questions about deployment, such as with XEN, openVZ or other para-virtualization instances, for example, don't hesistate to email me!