a bug i found in query.php that not allowing exclude multiple authors when calling query_posts.
when parsing the author element it only take the first author in the list and exclude it.
author=-21,22,23 --> only exclude 21
i track down it to this line
$q['author'] = ''.intval($q['author']);
change it to this
$q['author'] = $q['author'];
i think it need fixing?
all the best,