Version: (using KDE 4.4.1) Installed from: Debian testing/unstable Packages Use case: User wants to generate his wallpaper using an external program. Plasma detects that the wallpaper has been changed by the program and reloads it.
I think this feature has been implemented for quite some time. http://quickgit.kde.org/?p=kde-workspace.git&a=commit&h=78ed1699e8e73527d763996cdacdfc97f3557d0f