GNOME and KDE are great, but they are a little heavy. If you're on an older system, or you just want a change of pace, you can use other window managers under Ubuntu, such as Fluxbox, XFCE, and Enlightenment.
If there's one thing that's great about Linux, it's choice. If you don't like a particular program, there's a pretty good chance that Linux has at least one alternative. This even applies to your entire desktop environment. The desktop environment comprises a lot of different programs, such as a window manager (which handles drawing borders around your windows, moving them, and so forth), panels so you can launch programs, background-management programs, and more. The most popular of these desktop environments are GNOME and KDE. Ubuntu defaults to GNOME [Hack #15] as its desktop environment but also offers a Kubuntu alternative [Hack #16] that automatically defaults to KDE instead.
If you don't particularly like GNOME or KDE, you still have other options. Linux has a large number of window managers that you can use instead of a full desktop environment such as GNOME or KDE, and all of the popular ones are available for Ubuntu. There are a number of reasons why you might want to give some of these window managers a try:
Both GNOME and KDE need a fair amount of resources to run. Most of the alternative window managers require substantially fewer resources, so they might be attractive if you are using an older computer or if you just ...