KDE & GNOME

Architecture :
Desktop Environment (KDE/GNOME)
|
Window Manager
|
X Server (X.org/XFree.org)
|
Kernel

KDE
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- Memory consuming (but very user friendly)
- use QT library but may not free (http://trolltech.com/products/qt/licenses)
- Very suitable for home users - full multimedia support.
- Highly customisable for window environment settings.

GNOME
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- Efficient memory usage (simple & fast)
- uses Gtk library, is free & part of GNU project (http://www.gtk.org/)
- chosen by major enterprise linux distributions (Redhat,Suse,Fedora,Debian,CentOS)
- Highest distribution due to popularity of Ubuntu (http://distrowatch.com/)
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Both of them still having problem to display XGL (3D Desktop Effect), example, window title missing, task panel can't show currently opened application, and some pop-up window show blank, completely black.

Also, OpenOffice Calc 2.x cannot run in 3D Desktop Effect properly.

After enabling 3D Effect in GNOME, the window manager tool will be shown and can configure window behaviour.

In KDE, windows behaviour settings are available even 3D Desktop effect not yet enabled. Thus, KDE can easily change back to old settings, when 3D effect is not working fine, but GNOME can not do that.