Script Summary: Changes the background color of links which are in a user's del.icio.us bookmarks to prevent creating duplicate bookmarks.
Designed to help stop the creation of duplicate bookmarks on del.icio.us Any link that is already in a user's list of bookmarks gets a grey-ish background. Still a very simple, but working, version.
After installing, open a new window or reload. Then, right-click on the greasemonkey logo in the menubar or go to tools-greasemonkey, select "User script commands..." and then "Fetch del.icio.us bookmarks". Enter your account name in the dialog. That's it. The list updates automatically when you add new bookmarks, or at least it should. If it doesn't, just fetch them again. This does now fetch all your bookmarks.
The other commands are pretty self-explanatory. You can remove a url or all urls, as well as list the urls it checks for.
The script has an updater, which checks once a week for a new version. If there isn't one, that shouldn't interfere with anything. If it is, I highly recommend you download it.
Installing the script also has the side effect that all your links on del.icio.us have the grey background color.