We have been building professional websites using Drupal for well over 4 years now, and html based sites for over 10 years!). Drupal has come a long way since version 4. From a rough and tumble roll-your-own fledgling content management system to its current beautiful, user friendly, powerful incarnation in Drupal 7, this is one CMS that has blossomed significantly.
We were originally drawn to it while testing just about every major C.M.S. back in 2006 (something we continue to do!) and it stood out, even back then, as the one with the most potential.