Download script: http://www.devoresoftware.com/gm/grks/grkillstars.user.js. Also available on the userscripts.org site at http://userscripts.org/scripts/show/89903.
A request was posted on Ask MetaFilter for a script to clear starred items in Google Reader. I wrote the Greasemonkey script Google Reader Kill Stars to address the problem. When activated, the script clears all stars in Google Reader for items loaded in the main items pane by simulating mouse click on each starred entry. After Google Reader is loaded, from the browser menu choose Tools/Greasemonkey/User Script Commands/Remove Stars in Google Reader to clear all those pesky stars from loaded items.