Scenario:
"I want to change the way my comment form looks (e.g. customise it with different words on the button, etc) but all I can find in the skins is this <%commentform%> thing. Where are the source files for this?!"
Solution:
The code for the comment form is stored in the following files in the /nucleus/forms directory:
commentform-loggedin.templatecommentform-notloggedin.templatecommentform-closed.templateOriginal forum thread (thanks, ftruscot!):
http://forum.nucleuscms.org/viewtopic.php?t=13078