The folks at WordPress like to say "WordPress is both free and priceless at the same time." We don't know about that 'priceless', but it is one heck of a tool to have in our development box. Depending on the project scope, budget and design, sometimes WordPress setup on a LAMP platform is a perfect fit for the goals of the client.
We especially love that it is quick and easy to install and quite extensible. The code is especially light and with over 16,000 plugins as of fall 2011, expanding WordPress' out-of-the-box functionality is easy and inexpensive.
If we don't need to customize an extranet or build a comprehensive public website with 5+ content managers, WordPress is often the first possibility for framing up a nice web application.