Sounds interesting : Spamgarden

Spamgarden is a WordPress plugin that takes random words from your recent comment-spam, and uses them as fertilizer to grow your own private Spamtree.

How to use it:

  1. Download the Spamgarden plugin.
  2. Upload these files into your wp-content/plugins directory, in their own /spamgarden/ directory.
  3. Activate the Spamgarden plugin in your WordPress admin panel.
  4. If needed, adjust the settings for Spamgarden under Options.
  5. Add to the post/page where you want the spamtree to appear.

You can see it in action at Netlash Spamgarden.