Creating your own theme in Drupal is certainly challenging due to the dynamic nature of the content and all of the different content areas that need to be designed. Websites should utilize Div tags and CSS as opposed to tables and inline formatting.
One of the best examples of what can be done with CSS can be found on the Zen Garden website. The Zen Garden principals have been adapted to Drupal through the use of the Zen theme. Control over the design of the Drupal site is controlled by changing the CSS.
This project describes how Zen for Drupal works and how you can design your own sub-theme.