"leave feedbacks" or "comments" depends on your skin.
take a look in folder blogs/skins/the_skin_you_choosed/ for files _item_comments.inc.php and/or _item_feedback.inc.php
edit the files and search for the words you wanted to replace.

Here's my blog: http://autismepicenter.net/blog/blog2.php

I still can't find the spot I need to change. I checked in _item_comments.inc.php and _item_feedback.inc.php. I also copied the latter into my skins directory, uploaded it, and it crashed my blog's comments page.

Can anyone offer a more exact answer?

If you go to my blog it's the "Send feedback" right next to each post that I want to change to say "Leave comment".

Thanks!

came across your post since I had the same issue. After looking around for a while I found the answer. It depends on which skin you are using but for me I am using the evopress skin and the file I had to edit was the _item_block.inc.php file. In that file there is the following:

<?php
// Link to comments, trackbacks, etc.:
$Item->feedback_link( array(
'type' => 'feedbacks',
'link_before' => ' | ',
'link_after' => '',
'link_text_zero' => '#',
'link_text_one' => '#',
'link_text_more' => '#',
'link_title' => '#',
'use_popup' => false,

Simply replace 'feedbacks' with 'comments'
make sure you use lower case 'comments' and not 'Comments' or you will receiver an error as I found out earlier. Hope this works for you.

/inc/items/model/_item.class.php

line 2252:
if( $params['link_text_zero'] == '#' ) $params['link_text_zero'] = T_('Send feedback').' &raquo;';