I've just installed Subscribe to comments Reloaded plugin.
I have disabled default checkbox, and put the
<?php if (function_exists('subscribe_reloaded_show')) subscribe_reloaded_show(); ?>
code line in my comments template.
The Subscribe to comments form shows up when I'm connected (as the author of the article) I get the "Manage your subscriptions" link. But the form doesn't show up as soon as I log out (ie my visitors don't see it).
When I check the html code logged out I get only this:
<!-- BEGIN: subscribe to comments reloaded --><p><label for=<!-- END: subscribe to comments reloaded -->