I've got a plugin that does this ... I'll have to dig it out .... but there should be something similar in the core .... soon :p

¥

*edit*
You probably don't want the whole of the plugin, so this is the relevant bit :

	/**
	 * This is a blogrum function
	 *
	 * @param unknown_type $params
	 */
	function AfterCommentFormInsert( $params )
	{
			$params['Comment']->Item->set( 'datemodified', $params['Comment']->get( 'date' ) );
			$params['Comment']->Item->dbupdate();
	}

Cool! Thanks again! I'm not a fan of doing (a lot of) core hacks (anymore), but hey once you start you might as well go for it right?

ideally there would be an additional field in the db (updated by the core) named sth like:

post_datetouched
ot
post_dateamended

which do you think is best?