Sounds a good idea..
http://www.nytimes.com/2006/03/30/te...83a3c9&ei=5088
I can think of one other major problem though. It currently only fully supports Outlook or Outlook express on Windows.
Anyone using another email client, or platform (such as a Mac or Linux) will (at the moment) have to go to the product's web page to label things as spam or not spam.
Still, I am sure that problem will be solved either by Spam cube or a third party plug in before long.