Not all spam is sent to us as some has malware that would bring down many blogs when opened. You can locate your spam here http://http://asthe1above.wordpress.com/wp-admin/edit-comments.php?comment_status=spam
If you get spam that slips by Akismet then mark it as spam (do not delete it) and over time Akismet will learn it's spam.
If you get dalse positives then approve them and Akismet will learn.
Over 80% of all comments submitted to WordPress.com blogs every day is spam. On the spam that Akismet catches it takes only seconds to click "empty spam" and you don't even have to click "empty spam" if you don't want to. Akismet will maintain comments it has caught for 15 days from the time they were received, and then it will delete the comment automatically.
For more information please take the time to read "5 things every blogger should know about spam" on this page Akismet: How it works http://akismet.com/how/