And now it's the turn of Drupal - the much mistaken CMS. I like to think of it not as a content management system, but as a web framework with modules. To the first time user it is a confusing barebones system with not a lot of flexibility, until you find all the modules and work out which one does what.
This leads to two types of people - those who have used Drupal, got confused/frustrated and now use Wordpress.. and those that struggled on up the steep learning and now love it.
Here's a perfect example - you install Drupal and soon realise that when you add a new post or article it's just plain text (or you have to add HTML tags manually) there is no WYSIWYG editor by default. Some people will give up and grumble - others will search for the the correct module, install it and be happy.
If you use Drupal for every project you will learn the "Drupal way" of doing something. You will have your core modules that you always use and know how to configure them. You will tinker with the settings and add functionality. A site can easily have twenty or more modules added to the basic drupal install to get it working - and these all may need updating and maintaining over time.
Theming drupal is also an art form. The new code bits that need to be slotted in to take an HTML design into a usable drupal template are a bit of a mind bender - again something that gets easier the more you do it.
Check out drupal.org for the official website, download and tutorials to get you started.
Here's an interesting video interview that is a good introduction to Drupal and what it's capable of doing.
Conclusion. Drupal is like any other sophisticated software - you need to learn it, and understand how it works. It's not really for the one time user or first time designer. BUT once you get it working once (this is the hard part) and document/remember what you did, then the next time it gets easier. If your going to be using it multiple times and want all the flexibility of professionally developed modules for ecommerce, social networking, blogging and multimedia it's great.
Here's my passing comment, more of a warning - don't try to learn web design (html, css, php) AND start to use drupal at the same time. You will become confused! This is a tool for web designers/developers who already have a firm grasp of the basics.
For more CMS reviews check out these posts.