Version: (using KDE KDE 3.4.2) Installed from: Unspecified Linux Kicker in 3.4.2 has a "show desktop" button that shows the desktop when you click on it, but if you click on any folder, all the applications are restored. A minimize all button would keep all the applications minimized so the user could interact with the desktop and accomplish a task and not be cluttered by all the applications currently running. Note, Windows does provide this feature, right-click on Start Menu and the option is "Minimize All". In Windows, if Minimize all is used, then Unmimize all can be used to restore things to their previous state.
This was exactly what the show-desktop button has done for (at least) the last 4 years, until recently. Unfortunately, (as described in Bug 108899), a new (mis-)feature has been introduced, and there is no workaround for it.
Kicker is currently unmaintained, you can look to your distribution for help, however.
If you look here: http://www.richardneill.org/src/kshowdesktop.tar.gz you'll find a really ugly hack that I wrote, which provides a perfect workaround.