Observer Tests a test suite of all the available observers in SketchUp.
The image shows the menu with the observers. Click an an observer to add it to the model. Be sure to open the Ruby Console window to view the events that get called.
The latest version includes all the Observers in SketchUp. A few of them need some user input to find something to attach to, and so I added some dialogs to help pick those things out. These are marked with an asterisk.
To install, unzip the file and move the observers folder into your Plugins folder. The Observers menu will appear in the Plugins menu.
Download from here.