Over the past decade, Linux has emerged from a herd of obscure and nerdy operating systems to warrant a place in even the most technologically unsophisticated business environments. And in the past three years, a few distributions have made stupendous leaps in performance and usability, winning the affection of millions of mainstream desktop users.

The recent releases of Ubuntu 8.04 and Fedora 9--two top Linux distributions--mark another step forward in the evolution of the Linux desktop. I've been running both of them to see which offers the better blend of usability and advanced features.

Ubuntu 8.04 Hardy Heron
Since the release of version 5.10 (aka Breezy Badger) in 2005, Ubuntu Linux has stood apart from hundreds of other Linux distributions, capturing the attention of penguin heads and of users seeking a free, stable, usable alternative to Microsoft Windows. With its click-and-go Live CD installation and its support for a broad base of hardware devices, Ubuntu built a reputation for ease of use that changed the way many people think about Linux. PC World was so impressed that Ubuntu landed on our list of "The 100 Best Products of 2006," a first for any flavor of Linux.

The latest version of Ubuntu, 8.04 (aka Hardy Heron, or just Hardy for short), builds strongly on the foundation laid by its predecessors. This release is a Long Term Support edition, to be supported until April 2011, and Hardy Heron shows more polish and refinement than any other Linux distribution I've seen.

The operating system comes packed with new features, beginning with a revised kernel (2.6.24), the latest version of Xorg (7.3), and the most recent Gnome desktop interface (2.22.1). On top of these advances, Hardy offers several new default applications, including Brasero for CD/DVD burning, the Transmission BitTorrent client, and Vinagre virtual network computing software for remote desktop viewing. You also get support for enhanced security via SELinux (Security-Enhanced Linux)--but in Ubuntu 8.04 it's not installed by default, as it is in Fedora 9.

From the get-go, the Hardy Heron experience is smooth. I installed it on several machines, including an aging laptop with a Via graphics controller that's notorious for making a hash of things in Linux. Each installation found and recognized all of my hardware without requiring a reboot. Even my media card slot, which Windows can never locate a driver for on its own, worked right off the bat. Existing Ubuntu users enjoy even slicker installation: The Hardy Heron upgrade comes through the Update Manager, and one click initiates a totally automated --albeit fairly long--upgrade process that leaves all of the user's data in place.

Ubuntu's automated Hardware Drivers utility seeks out proprietary drivers for devices in your system, simplifying the task of grabbing the latest proprietary nVidia driver, for instance, so that you can enable Desktop Effects. Some hard-core open-source advocates disapprove of Ubuntu's compromise with the closed-source world, but end users who care more about usability than ideology will find this arrangement a boon.

Apart from the new default apps, Ubuntu hasn't changed much in overall look and feel this time around. Sure, there's artsy heron-themed wallpaper, but longtime Ubuntu desktop users will find little else to poke at in this version. That development indicates that Ubuntu has matured to the point where it can focus on refining its feature set rather than massively reworking its elements in each new version.

The changes in the default apps seem judicious rather than sweeping. Brasero, for instance, is a far more complete disc-burning utility than Serpentine, the relatively simple CD burner found in previous versions of Ubuntu.

Hardy Heron still lacks a few features that I had hoped to see as defaults by now, such as a Desktop Effects Manager for Gnome. Downloading Compiz Configuration Settings Manager through apt-get (the command-line tool for handling packages) isn't hard, but it should really be there in the first place. Without it, newbies have no idea how to turn on the desktop cube they've heard so much about. Also still absent is a decent theme manager to take advantage of Desktop Effects.

Minor quibbles aside, Ubuntu 8.04 is the best-assembled and most polished Linux distribution I've ever used. Ubuntu 8.04 performs well where Windows XP and Vista screech to a halt, particularly on older hardware. And since it comes with OpenOffice.org, Firefox, Evolution Mail, and a host of other apps right out of the box, it may be the best way to breathe new life into a seemingly moribund PC.

Fedora 9
Fedora was born as an all-open-source alternative to the business-centric Red Hat Linux. As such, it enjoys a solid legacy of Linux development. Unfortunately, as the nonprofit cousin of a major commercial distribution, Fedora doesn't always seem to get the attention it deserves. But last year, Fedora doffed the shadow of rival Ubuntu by releasing of Fedora 8, which offered a simple, graphical installer and the best hardware support we'd seen from the Fedora distribution. Nevertheless, it lagged behind Ubuntu in ease of installation and overall usability--largely because its commitment to Free and Open Source Software (FOSS) left it without complete drivers for some major hardware, including nVidia and ATI cards and various wireless cards. Any astute Linux user could add these, certainly, but the process was too geeky for average Joes who just wanted to give Linux a try.

With version 9, Fedora has stepped up its ease-of-use game. Gnome 2.22 brings a host of great new features, including support for Webcam videos. A prerelease version of Xorg 7.4, however, causes problems with nVidia cards, preventing Desktop Effects--which is now standard in Fedora 9--from working. At posting time, this problem remained unresolved, though contributors to the Fedora Forums suggested that it would soon be corrected. Fedora 9 also has a newer kernel (2.6.25) than Ubuntu 8.04.

One of the most important changes in the new Fedora is immediately visible: its Anaconda installer can dynamically resize NTFS hard-drive partitions, making the task of adding Fedora to existing Windows installations much easier. Ubuntu users have long enjoyed a similar feature, so it's nice to see Fedora catch up. Another new feature of the installer is a one-click option for drive encryption. Overall, Fedora's revamped install routine is the distribution's best yet, and it nearly matches Ubuntu's in simplicity and ease of use.

I liked Fedora 9's new PackageKit, a graphical interface for Fedora's Yum update utility, too. PackageKit is the nicest update manager I've tried in Linux, with big, friendly icons for bug fixes and security updates. Also, like Ubuntu 8.04, Fedora 9 now uses PulseAudio to control sound devices throughout the OS.

By default, Fedora includes SELinux, which enforces security policies throughout the OS. Developed by the U.S. National Security Agency, this app does an excellent job of alerting users to potential security threats and managing user authentication. Most users will find that the biggest benefit of SELinux is its management of root user authority: The program alerts you when you've had root privileges activated for more than a few minutes, so you can minimize your exposure from this vulnerability.

For users who are already familiar with Linux, Fedora 9 is an excellent choice. Robust security features and installation options make it somewhat more versatile than Ubuntu, which offers a more streamlined (and therefore more restricted) installation. For most users, though, including millions interested in trying Linux for the first time, Fedora lacks the polish and ready-to-run simplicity of its more popular rival.

Ubuntu 8.0.4 offers a level of functionality comparable to that of Mac OS and Windows, from delivery to installation to daily use. Unfortunately, the ties that bind all Linux distributions--primarily a lack of support for major Windows- and Mac-based business, design, and gaming applications--still hold Ubuntu back from mass popularity. For users with such moderate computing needs as Web browsing, e-mail, and basic document creation, however, Hardy is a compelling option.