Since compositing window managers are the latest craze for dragging down system performance, perhaps no one should be surprised that KWin, the KDE windows manager, adds its own special effects in the desktop's newest version. Available from System Settings -> Desktop -> Desktop Effects.
The available effects tend to be under-documented, but, as the hint at the top of the window suggests, you can usually figure out what each does by its settings. The effects vary from the cosmetic (Dim Inactive Windows, Translucency) through the frivolous (Explosion, Fall Apart), to the practical (Magnifier, Zoom).
Many effects require a keyboard layout with a meta key (an additional control key), and enabling special effects is a noticeable drag on system, even with a gigabyte of RAM. Still, I suspect that more will be written as KDE 4 moves through its release cycle. Meanwhile, KWin has made a good start in variety and usefulness.
This list only begins to describe some of the features of the new KDE. A desktop by definition is a large application. And when as many changes have been made as in KDE 4, you can fill two thousand words just listing them. I could easily have replace some of the items here with mention of the Lancelot menu widget, the Gwenview graphics viewer and the Okular document viewer, the Dolphin file manager, or any of dozens of other possibilities.
But why spoil your fun? KDE 4 has lot of room for improvements, and the odds are that it won't completely fill its potential until about version 4.3. Meanwhile, what's already in the new version pushes at the borders of usability and desktop design from every angle imaginable. Besides being a polished environment for routine work, KDE 4 is probably the most interesting program to explore since OpenOffice 2.0, so enjoy your own journey on the route. You're sure to find things that annoy you, but even more that you'll appreciate.