For the sake of simplicity, my question is focused specifically on Wordpress instead of focusing on all Content Management Systems including Joomla, Drupal, Concrete5, or you-name-it.
Wordpress is becoming ever more popular. You can extend it's feature set with widely available plugins or you can simply design your own plugins if you know a little bit about programming. There are more and more "big" (read well-known, famous or credible) websites that are built using Wordpress. For some examples, take a look at this link.
Abraham Maslow once said, "It is tempting, if the only tool you have is a hammer, to treat everything as if it were a nail." I see this tendency within the community of Wordpress developers, and while I value their knowledge and advice on what can be done using Wordpress, I'm afraid that asking them my question about "when to use Wordpress" will only be met with a blank stare that says "is there a time you would not use Wordpress?" This fact is very visible when you do a google search for "when to use wordpress". The situation does improve slightly if you search for "when not to use wordpress".
So my question is, in this year 2011, what criteria should best help a web developer determine whether or not to use Wordpress for a given project?
After some more searching I found this excellent post on this topic: http://wordpress.stackexchange.com/questions/10594/when-should-we-not-recommend-a-client-use-wordpress