I get a lot of Google requests like "/node/comment/reply/13". This URL is invalid (it should be "/comment/reply/13"), yet invoking it returns the main page and a status of 200: OK. This leads to duplicated content, which is penalized by Google and others.
I suggest to instead return a 404: Not Found, this is because the page requested was - well - not found, actually.
To achieve this, lines 2109p in node.module have to be changed from
> drupal_set_title(''); return node_page_default();