Works well and it gives some very useful information especially if you have a lot of widget areas.
Would you be able to add a way to toggle it on and off without deactivating the plugin or logging off? Often I want to view the site in the browser and I only need to see the widget area names for a second. Then I'd have a more accurate view of the site when I don't need the info.
If there was a checkbox on the top admin bar, it would save several steps. Great plugin.