I have a test installation of plone installed on my linux server at http://localhost/plone.  I installed qPloneComments and went to the setup page and I was getting 404s when I clicked the save button.  The <form> action url that was being generated was:

/plone/plone/prefs_comments_setup_form (bad)

instead of

/plone/prefs_comments_setup_form (correct)

To fix, I edited qPloneComments/skins/qplonecomments/prefs_comments_setup_form.cpt

under:

        <form name="edit_form"

I changed

              tal:attributes="action string:${here/getId}/${template/getId}">
-to-

              tal:attributes="action string:/${here/getId}/${template/getId}">

Charlie

I also made the same change to prefs_recent_comments_form.cpt

Ditto.  I just applied the same fix, and actually came here to report the bug, only to find this thread instead.

The latest svn trunk is still the stock 2.3.1, so this fix must still be applied manually.

[UPDATE]  Actually -- the fix described in the original post was not adequate.  When I tested it on my live site, which is exposed through apache rewrites, the '/${here/getId}' includes a part of the internal plone path that is inappropriate.

I changed the line to the following, which works under both circumstances (direct :8181 access, and apache-exposed access):

tal:attributes="action string:${here/absolute_url}/${template/getId}">