It’s probably a bug when starting a topic that immediately gets flagged by akismet.
Adding a post to an existing topic will probably just come back with a missing post.
Since bbpress sets the status to “2”, it will be treated like a deleted post/topic to the end user. Moderators and Admin will see deleted post indicators.
This is a pretty awful bug… users often repost the same message a dozen times in a row and get filtered over and over – and see that 404 error message each and every time! Then they get screamingly angry (usually at me haha).
Is this fixed in 1.0? Does anyone else get complaints from users about this?
I doubt they anticipated that. Years later, WordPress unbelievably still shows NOTHING when a comment is held in the moderation queue. You have to install a plugin to give the user some kind of clue what has happened. It’s dumbfounding.
It has not been fixed in 1.0-a6 (as of three weeks ago). It happens on WordPress.org too 
(And _ck_, what’s a good plugin for that on WP? I’ve yet to find one I like, but I’m picky.)
Ipstenu, my skip-akismet plugin works on wordpress installs too, though there is some kind of subtle bug I can’t seem to find where it doesn’t catch everyone on the wp side, works great on the bbpress side however.
If you meant what will notify users of comments being held, this will do it:
http://txfx.net/files/wordpress/notify-users-of-moderation.phps
What’s crazy is that was written back for WP 1.2, and yet it’s still needed, 5 years later.
Here is an untested variation of Mark’s WP plugin for bbPress, it’s a little more sophisticated in that it tries to return the person back to the topic they were in if it exists or if they were starting a topic, to the forum they were posting in.
<?php
/*
Plugin Name: Moderation Notification
Author: _ck_
*/
add_action( 'bb_post.php', 'moderation_notification', 999);
add_action( 'bb_head', 'moderation_notification_alert', 999);
function moderation_notification($post_id) {
if (empty($post_id)) {return;} // invalid post
$post = bb_get_post($post_id);
if ($post->post_status==0) {return;} // not moderated
if ($post->post_position>1) {
$link = get_topic_last_post_link($post->topic_id); // return them to the last known good post in the topic
} else {
$link = get_forum_link($post->forum_id); // return them to the forum that they posted in since there's no valid topic yet
}
$link=add_query_arg('moderated','true',$link); // set the flag
wp_redirect($link);
exit;
}
function moderation_notification_alert() {
if (!isset($_GET['moderated'])) {return;}
$out = <<<EOF
<script type="text/javascript">
<!--
alert ("You post was successfully processed, \n\n however it was placed on hold and will appear once a moderator verifies that it is not spam.\n\n Please be patient and do not resubmit your comment.");
//-->
</script>
EOF;
echo $out;
}
?>
You can see the notice by putting ?moderated=true on one of your urls
I don’t recommend trying to purposely cause spam to test it because akismet might flag you globally as a spammer and you’ll end up being bozo’ed across multiple forums/blogs.
