Display Custom comments field number

I would try something like this:

$comments = get_comments();
$yes = 0;
$no = 0;
foreach ($comments as $comment) {
    $vote = get_comment_meta ( $comment->comment_ID, 'vote', true );
    if ($vote == 'yes') {
        $yes++;
    } else if ($vote == 'no') {
        $no++;
    }
}
echo 'Yes:'.$yes.' No:'.$no;

Problem is the numbers can easily be manipulated so it might be better to count only one vote per user_id, comment_author or comment_author_IP depending on your usage.

Codex: get_comments – get_comment_meta