I have been developing for WordPress for about 3 years and most of that time has been creating templates. It wasn't until the latest release of WordPress (3.0.2) that I saw any need to build websites with it. Although it was a strong blog platform, for me it just wasn't mature enough to deliver on the promise that it would not cause me any more grief than it did in the early days when I was testing it. However it has come full circle and is now a major contender for creating fantastic websites. Although I still do not consider it a full fledged CMS and this is due to the limited amount of development being done with the plug ins (widgets). Lets face it in all reality WordPress is a Blog platform and a very good one at that. However I still hold my reservations that it can or should be considered as a full class CMS to develop websites that require more than a blog.
I have found it to be a fantastic application for marketing professionals and for anyone who needs a nice brochure type website. Consider WordPress only if you know you will not need it to be anything more than a Blog, tool or a simple marketing platform. If you do need something that will grow with you and can be molded into more at any time, I recommend Joomla for your ultimate web design platform.