Here at Kangaroot, we've been running the Belgian mirror for the Arch Linux distribution for quite some time now. Some time ago, a coworker at a client's location seemed really enthusiastic about it, so our Nils Cant thought he'd give it a whirl himself. Here's what he thinks.
"The main idea behind Arch: provide a distribution which keeps things as simple as possible. A good example is the way they replace the classic sysv init system with a simple array of values. No upstart, no systemd, no tools necessary to create start/stop symlinks. The order in which you place the names of the init scripts, is the order in which they are started. Simple, no?
Arch Linux is a distribution which performs "rolling updates". Unlike Debian or CentOS, you don't have "version X" installed. If you choose to regularly update your packages, you're always running the last available version. This gives you a cutting edge operating system, which might not always be suitable for server use, but is definitely cool for a desktop machine.
Building your desktop environment is similar to Gentoo or a minimal Debian install. After the install is finished, you end up with nothing but a command-line, and it's up to you to choose a Desktop environment, install your applications one by one, and manually enable each and every feature that you want. This is a lot of work, but luckily Arch has an awesome wiki, with tons of information on how to get stuff working.
Pacman, the Arch package manager is great as well. If you've ever complained about yum being slow compared to apt, prepare to be amazed by pacman.
Running Arch Linux as your main desktop OS won't be the easiest road to take, but it is definitely one of the coolest."
Update: as of October 2012, systemd is now the default init system. Systemd is a system and service manager for Linux. It provides aggressive parallelization capabilities, uses socket and D-Bus activation for starting services, offers on-demand starting of daemons, keeps track of processes using Linux control groups, supports snapshotting and restoring of the system state, maintains mount and automount points and implements an elaborate transactional dependency-based service control logic. It can work as a drop-in replacement for sysvinit. Because of the change, initscripts are no longer available on the live system.