Google Reader Notifier displays a small icon in the browser's bottom right corner, telling you how many unread items you have in Google Reader. It also shows a small notification window every time new items arrive to your feeds. The icon can also be used as a shortcut: left click on it and it will open Google Reader in a new tab.

The extension only displays the total number of unread items, so if you have many of them to read it's not that useful. Maybe it would be nicer to see the number of new items being added to that total list each time the extension checks Reader.

Google Reader Notifier features some configuration settings that allow you to control the way it behaves and also customize its appearance. In short, I think this extension offers something that I personally missed in Reader (some kind of notification tool) but it could also be improved in the way it announces new elements.