The warning when emptying the trash!
It is actually possible to get rid of the warning when emptying the trash in the Finder preferences. Most people don't realize that the Finder actually has a separate preferences window. I guess we always assume that everything about the Finder is done in System Preferences. "Preferences..." is actually right there in the "Finder" menu. That is where you can disable the empty trash warning in the "Advanced" tab. It think getting rid of this warning really makes sense now that everything is backed up and fully recoverable with Time Machine.