There is an easy way to get the latest version of commentluv to work with cforms.
You don't need to add the custom checkbox for it.
Just go to the commentluv settings page and enter the names that cforms has assigned to the fields. On mine it is:
name:cf_field_2
url: cf_field_4
comment text area: cf_field_5
to find out the names, you will need to view the source or if you use firefox click and drag over the form fields and right click and choose "view selection source" to see what values are in the <input type="text" name="cf_field_2" html lines
sorry about the ID pull down box not updating on this version, it is a minor bug that will be fixed on the next update. This version doesn't use ID any more anyway and i'll remove those options on the next update.
you can submit a support ticket at http://www.commentluv.com/helpdesk if you get any problems