What does this mean for Drupal Gardens users? Just what you'd think. You receive the best spam protection available on the web from Mollom. There is no setup, no hassle, and no cost.
What does this mean for developers? A great example of how to provide Mollom to your customers, in the form of the Mollom API module for Drupal. The Mollom API module was developed by Jacob Singh and Gábor Hojtsy from Acquia. The Mollom API module uses Mollom's Reseller API to automatically provision the service and to programmatically obtain public and private keys for each Drupal Gardens site.
— Dries Buytaert