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Anyone who has worked with both knows that anything you can do in WordPress, you can do in Drupal, and vice versa. It just takes some elbow grease.
I am a huge advocate of WordPress as both a personal blogging engine and a multiuser CMS. It is easy to setup and theme, has a largely backed community, and has an extensive selection of plugins (with great focus on SEO and social blogging) making it an excellent choice for sites of any size.
Drupal is still regarded as the Best Open Source PHP CMS, though, and is commonly used by large corporations, government, and universities. Drupal has a large following and plugins for nearly any operation as well. It is a great thing to learn because of its broad market, but WordPress developers might find some difficulty getting acclimated—Drupal has a much higher learning curve.

This information in this article pertains to WordPress 2.8+ and Drupal 6.15. Here are some tips/parallels that may help you as a WordPress user jumping into Drupal.

Installation

The installation procedures of Drupal and WordPress are similar, but there are a few operations you have to perform manually in Drupal:

WordPress has greatly simplified its installation procedure by automating the creation of the wp-config.php file based the the wp-config-sample.php file. Drupal has yet to do this up—you have to manually create the settings.php file in the sites/default folder by creating a copy of default.settings.php and renaming it.

A vanilla WordPress install in simple given that the directory structure is created for you. In Drupal, after you first upload the files, you have to create additional directories. From your root, go to the sites/default folder and create a files folder. Make the folder writable if it isn’t already (see the Drupal status report).

I also recommend going to the sites/modules folder and creating folders called contrib and custom. Put modules you download from Drupal.org into contrib and modules you create into custom.

Theming

Here is a table of Drupal theme file and folder equivalents:

The similarities in theming begin to diverge at page.php/index.php. From here, Drupal uses different files for “nodes,” “blocks,” and optionally “panels,” “contexts,” “views,” and so on depending on what modules you are using.

Let me know if you have any more useful parallels to draw. I hope this helps you make sense of things—I know it would have helped me when I started.