Something I haven't discussed much over the years is Ubuntu's usefulness on servers. The original idea behind Ubuntu was to take Debian, a super-stable distribution that's always had more success on servers than desktops, and polish it up for desktop use, with easier installation and configuration and a quick, regular release cycle.
That Debian heritage still underlies the project, though, and for a few years now Ubuntu has been trying to target the server market as well. I still run Debian on my servers, and the main reason is the release cycle. I don't have any servers that need to be updated every six months, so the LTS releases are the only ones that I'd feel comfortable running.
While you're meant to be able to upgrade directly between LTS releases, skipping all of the six-monthly releases between them, I have to wonder just how much time and effort goes into testing that upgrade path, with the constant time pressures that the developers are under.
Debian's approach of releasing ‘when it's done' is definitely less predictable than Ubuntu's - Debian 5.0 ‘lenny' was meant to be out six weeks ago as I write this, and it's quite possibly still not out as you're reading this - but it does lead to rock-solid releases, where every key piece of software, and the upgrade path between releases, has been extensively tested.
I'm definitely going to be keepinga closer eye on Ubuntu's progress in the server market from now on, though. The Wikimedia Foundation recently announced that it was standardising on Ubuntu across its farm of several hundred servers, replacing a blend of OSs that included Red Hat and OpenSolaris.
I've installed an Intrepid server to play with and so far, I'm quite impressed. The installer is a nicely streamlined version of the Debian text-mode installer, and it lets you enable a number of specific profiles, like ‘Virtualisation host' or ‘PostgreSQL server', that install extra functionality on top of the base packages.
It's definitely still designed for experienced admins, though - there are no GUI packages on the CD, so regardless of what options you select, you'll be staring at a plain text login screen once your system boots.
That might sound unfriendly compared to a Windows server, but frankly, I wouldn't have it any other way.