WordPress grew out of the need for personal publishing systems, and while it serves medium sized communities well, it excels for individuals and small groups. It's a good CMS to start with because its default functionality is robust without being burdensome for the average user.
WordPress's strengths are its ease of use and ability to add specific functionality via plug-ins. Its weakness is that it can be over-used. It's a good baseline for developing a highly unique website, but it's not as customizable as Drupal or Ruby on Rails. It is also known as the most SEO friendly content management system.
We've used WordPress for a number of sites where the content is the main focus. It's a great landing platform for funneling users into more complex online applications or processing systems.