Ben Collins ♦ was making some changes to the comment system and something he did caused the userscript to stop working (ref. 1, ref 2). The author of the script, Benjol, is aware of the problem and AFAIK is working on a fix.
Several (one, two) workarounds have been suggested until the issue has been resolved.
Tim Stone said he might be able to give it a look as well.
update august 12
The issue has been resolved in a recent update to the script.
For more information see this answer http://stackapps.com/a/4241/14817
