I’ve just figured out how to post from my shared items in Google Reader (and this blog) to my Facebook profile. Log in to Facebook and click on the profile tab. Under the “share” button is a “settings” link. Click on that link and you should see the Google Reader option there (and Digg, Pandora, Blog/RSS, Flickr, Picasa, and much more).
To find the public link to your Google Reader shared items go to http://www.google.com/reader/view/user/-/state/com.google/broadcast and look for the text that says “Your shared items are available publicly at this web page“