Cloudmark have a community facility to identify mail as spam or newsletter. When a spam message comes in users press a button to say that it is spam or newsletter. This then sends relivant information on the mail to cloudmark so any other users that get the e-mail have it automatically classified into the spam folder or newsletter folder. Obviously this would need to work on a points system as users idea of what is spam probably varies. Don't know if this is too envolved but it would be an excellent feature and should be highly accurate.