It looks like the site is down. And possibly gone forever. (?) However, you can still access the last snapshot or so from this URL:
https://web.archive.org/web/20140506043023/http://userscripts.org/ Via the Internet Archive Wayback Machine. -- You received this message because you are subscribed to the Google Groups "greasemonkey-users" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/greasemonkey-users. For more options, visit https://groups.google.com/d/optout.
