WordPress is one of the most versatile content management applications out there. Granted it won’t run a mammoth site, Dupal is much better suited for that, but WordPress is a solid workhorse that is fully scalable.
Now for those who would want to create a WordPress theme, we recommend the Ultimate WordPress Theme Tutorial at ThemeShaper.
WordPress themes are easily modified and the Codex offers a wide range of functions you can code into the heart of the site. Start with 10 Useful WordPress Loops Hacks. We also recommend this handy WordPress Cheat Sheet. Resources are also aplenty, but our favorite article so far has been Steffan Antonas’ 100+ Killer WordPress Resources.