Debian and Ubuntu are distributions that lend themselves naturally to comparison. Not only is Ubuntu a continuing fork of Debian, but many of its developers also work on Debian.
Even more important, you sometimes hear the suggestion that Ubuntu is a beginner's distribution, and that users might consider migrating to Debian when they gain experience.
However, like many popular conceptions, the common characterizations of Debian and Ubuntu are only partially true. Debian's reputation as an expert's distribution is partly based on its state a decade ago, although it does provide more scope for hands-on management if that is what you want. Similarly, while Ubuntu has always emphasized usability, like any distro, much of its usability comes from the software that it includes -- software that is just as much a part of Debian as of Ubuntu.
So what are the differences between these Siamese twins? Looking at installation, the desktop, package management, and community in the two distributions what emerges is not so much major differences as differences of emphasis, and ultimately, of philosophy.
Ubuntu's standard installer places few demands on even novices. It consists of seven steps: the selection of language, time zone, and keyboard, partitioning, creating a user account, and confirmation of your choices. Of these steps, only partitioning is likely to be alarming or confusing, and, even there, the choices are laid out clearly enough that any difficulty should be minimized.
The limitation of the Ubuntu installer is that it offers little user control over the process. If you are having trouble installing, or want more control, Ubuntu directs you to its alternate CD. This alternate CD is simply a rebranded version of the Debian Installer.
Contrary to what you may have heard, the Debian Installer is not particularly hard to use. True, its graphical version lacks polish, and, if you insist on controlling every aspect of your installation, you might to blunder into areas where you can only guess at the best choice.
However, the Debian Installer caters to less experienced users as much as experts. If you choose, you can install Debian from it by accepting its suggestions with only slightly more difficulty than installing Ubuntu would take.
Both Debian and Ubuntu are GNOME-centered distros. Although each supports a wide variety of other desktops, including KDE, Xfce, and LXDE, they tend to be of secondary importance. For instance, it took six weeks for Debian to produce packages for KDE 4.4, while Kubuntu, Ubuntu's KDE release, has received relatively little attention in Ubuntu's efforts at improving usability.
Debian offers a version of GNOME that, aside from branded wallpaper, is little changed from what the GNOME project itself releases. By contrast, Ubuntu's version of GNOME is highly customized, with two panels, whose corners are reserved for particular icons: the main menu in the upper left, exit options in the upper right, show desktop in the bottom left, and trash in the bottom right. Ubuntu's GNOME also features a notification system and a theme that places title bar buttons on the left -- controversial innovations that are unique to Ubuntu (unless some of its derivatives have adopted them recently).
In its drive towards usability and profitability, Ubuntu also boasts several utilities that are absent from Debian. These include Hardware Drivers, which helps to manage proprietary drivers, Computer Janitor, which helps users remove unnecessary files from the system, and the Startup Disk Creator wizard. In addition, Ubuntu offers direct links to Ubuntu One, Canonical's online storage, and the Ubuntu One music store.
Theoretically, these extra features should make Ubuntu easier to use. And, perhaps for absolute newcomers, they do. However, for many users, the difference between the standard Debian and Ubuntu desktops will be minimal. These days, what determines the desktop experience is less the distribution than the desktop project itself. Ubuntu does usually make new GNOME releases available faster than Debian does. But if you are using the same version, your desktop experience will not differ significantly no matter which of the two you use.
Debian and Ubuntu both use .DEB-formatted packages. In fact, Ubuntu's packages come from the Debian Unstable repository for most releases, and from the Debian Testing repository for long term releases (see next page).