While I would argue that Drupal’s stand-alone software is inferior to its WordPress counterpart, there is no denying that the themebuilder in DrupalGardens.com is vastly superior to the WordPress.com theming system.
In addition to offering forums and some other fancy features for your website out of the box, the Drupal Gardens website creation tool has WordPress.com beat on the usability side as well. Kinda makes WordPress.com look like a stubborn, old dog.
Of course, WordPress.com has some nice stuff that DrupalGardens.com does not (better templates for one), but that should not stop it from putting the fear of Drupal into the WordPress.com market share.
Here is my 10-minute website on DrupalGardens.com.