Hopefully this will end the confusion regarding Akismet that has been expressed in number of threads:
1) Akismet cannot be turned off on WordPress.com. That is not an option. With over 750,000 spams caught per day on WordPress.com blogs alone, trust me, you want it to stay on.
2) Spam that sits in the spam queue for more than 15 days is automatically deleted. You cannot get it back. If you check your spam queue more often than every 15 days, you should not miss anything.
3) *ALL* comments that Akismet thinks is spam should show up in the spam queue, irregardless of how old the post is that receives the comment. For self-hosted .org bloggers, there is an option to auto-delete spam on posts older than 30 days. That option is not available here at WordPress.com. It may be in the future, but it is not currently. There was a point about 6 months ago where the "auto-delete on old posts" functionality was enabled here at WordPress.com. It was only on for about a month before we turned it off again. We may re-enable it in the future.
4) There appears be a bug that sometimes causes spam comments to either not show up in the spam queue, show up in the spam queue intermittently , or show up in the spam queue after some delay. We have received a few reports of this, but have not yet been able to replicate it. We will continue to work on this.
Please do not contact Akismet support about the spam count/queue issue. We are already aware of it and it is something specific to WordPress.com.