Here are some impressive implementations: http://www.drupalgardens.com/ http://openatrium.com/ http://groups.drupal.org/aegir-hosting-system http://developmentseed.org/ -> Their projects are cool http://drupal.org/project/modules?filters=drupal_core%3A87&#... -> Modules organized by usage. Go through a few pages to see some specific use-case modules. http://2bits.com/articles/presentation-28-million-page-views... -> Drupal is NOT slow when configured properly. www.whitehouse.gov is probably pretty cool.

I recommend http://sf2010.drupal.org/conference/sessions/state-drupal for an idea of where Drupal is today.

I'm curious what other HN people think about Drupal. Would love to hear.