As a PopFile fan, let me remind you that the Bayessian Filtering that it uses to classify spam and various personal topics of the received emails, work in a very similar way as this PM's system. Instead of punctuating every answer it asks you to assign a category to every received email.

In a few months the system has learned a lot. It can do very exact guesses of your possible classification. And you don't have to correct much of it, any more.

I wouldn't imagine what would it learn by having many levels of classification inside of PM. Say, a general level, fed by all the members, and then a personal level for each sepparate member... It doesn't have to classify spam, but your interests.

If you are curious about it, you should visit their forum for alternative uses that people create from their nice Popfile opensource!