Just spent 10 minutes trying to figure out where my object origins were. And why the camera and lights were on the ‘visible’ layer but I couldn’t find them. Then I found that I had saved the file with the ‘render only’ box checked in the properties panel. Me so silly.
Some fun facts I discovered while trying to find my origins was that you can select ‘visible layer’ in the outliner filter box. This simplifies things enormously. Also, for keyboard shortcut lovers, if you select an object and press M alt 5 it will move the object to layer 15 rather than 5.