We've just uploaded version 1.0 of our official Chrome extension for WordPress.com.
The extension adds an icon to Chrome's toolbar; the icon displays the number of unread notifications you have on WordPress.com, and when you click on it, it shows your notifications in a small popup. The popup also includes a "Press This" button you can click to start a new blog post based on the page you're currently viewing and a "Follow" button you can click to add the current site to your WordPress.com reader.
The toolbar icon will also turn blue when you're viewing a WordPress.com-powered site.
Try it out, and let us know what you think. How can we improve it? What WordPress.com features do you want instant access to from your browser's toolbar?