I like the idea of this addon. Allowing me to have easy to find and consistent way of logging out.
It might be just my taste, but I find this ribbon too "big" and little too attention asking. It would be useful to be able to make the ribbon more like a small box on the edge and to make it's position also moveable. Or having a addon-button for this as alternative option would be a equally effective option.
Also, note that on Gmail, the ribbon comes in way of the chat. Picture: (http://i.imgur.com/CFuEJgK.png) The red area marks the box the ribbon takes over. the ribbon takes too much space there and it's actual box isnt visibile. Having a small movable box would be greatly apprecieated for this case.With the addon-button and/or a smaller ribbon/box I'd give 5 stars to this addon.