Version: (using KDE KDE 3.97.0) Installed from: Ubuntu Packages OS: Linux I believe a sort of system where the settings are rolled back to the previous ones automatically when applying new settings would be rather useful, for example when I made a mistake and tried to apply some settings I did not want, I clicked cancel, yet the system did not respond well to that, and when I restarted the DE, the icons were different. So such a system would be useful to prevent users from losing their fine-tuned settings in case they made a mistake and clicked the wrong button.
If you change some settings in system settings and close the window it triggers a dialog that asks you to confirm the changed settings or discard them. After this you can always use the "defaults" button.