Arch Linux is a general purpose linux distribution that can be molded
to do just about anything. It is fast, lightweight, flexible, and
most of the parts under the hood are quite simple to understand and
tweak, which can make it a good distro to "learn the ropes" on. We do not provide any configuration helper utilities (ie, you won't find linuxconf in here) so you will quickly become very proficient at configuring your system from the shell commandline.
Arch Linux uses i686-optimized packages which gives us improved performance over some of our i386-optimized cousins. This means that Arch Linux will only run on a Pentium II processor or higher. We try to stay fairly bleeding edge, and typically have the latest stable versions of software.
Arch Linux uses the Pacman package manager, which couples a simple binary package format with an easy-to-use build system, allowing the users to easily manage and customize their packages, whether they be official Arch packages or the user's own homegrown ones. The repository system allows users to build and maintain their own custom package repositories, which encourages community growth and contribution.
Pacman can keep a system up to date by synchronizing package lists with the master server, making it a breeze for the security-conscious system administrator to maintain. This server/client model also allows you to download/install packages with a simple command, complete with all required dependencies (similar to Debian's apt-get).
Arch's official package set is fairly streamlined, but we account for this with a larger, more complete "unofficial" repository that contains a lot of the stuff that never made it into our main package set. This repository is constantly growing with the help of packages submitted from our strong community.
Arch Linux does not provide any official support, but you will find a lot of helpful people on our IRC channel and on our user forums. Chances are that some other Archer has had the same problem/question as you and it's already been answered. Ask around!
Arch Linux uses a "rolling release" system which works like this: We have two symbolic releases at any given time, Current and Stable. The Current release is always pointing to the latest and greatest packages. As soon as a package is updated it is part of the Current release, so this is one to follow if you want to stay very up to date. The Stable release follows the semi-regular snapshot releases and does not move until the next snapshot/iso has been released. For example, the Stable release will point to all packages on the 0.4 ISO until we release 0.5; then Stable will point to 0.5 packages. This is useful if you only want to update your system when a new release is available.
So, to sum up: Arch Linux is a workhorse distribution designed to fit the needs of the competent linux user. We strive to make it both powerful and easy to manage, making it an ideal distro for servers and workstations. Take it in any direction you like.