I recently switched my CMS to Drupal for my site www.thefitnesselement.net, and I'm completely shocked that a free CMS can function so well.
I was running Mambo and I thought that was pretty good, but I wasn't completely satisfied, and oddly enough, a reference to Drupal on the Mambo forums led me to Drupal.org. I hope they don't miss me too much...
Drupal is serving my needs so much better and it looks a lot smoother and more integrated and less like a bunch of modules stacked together like Lego's.
Once I got familiar with the "taxonomy" set up that Drupal has, I realized that it is a lot more configurable and customizable than Mambo. I am especially impressed by the customizable roles that can be aaisgned to users instead of fixed titles.
It's a lot prettier too. :)