Over the years I've progressed from HTML-by-hand -> crappy content management systems -> slightly less crappy content management systems. I would use whatever the client wanted or whatever I recommended would be the best fit for them. Over time, I realized that WordPress was the best fit for all of them. It's completely scalable from a small personal blog to an extensive corporate multi-user website. I've used it as a blog, content management system, intranet, event scheduler, bug tracker, forum, social network, wiki, ... The API is very well written and very powerful, and it's getting better with each release. I can't name a single other CMS with an API that's even close to the same quality. Any layout a graphics designer makes in photoshop can be converted to a theme, and any functionality that's needed in a plugin/theme can be written by a programmer.
I started exclusively working with WordPress a long time ago and have never looked back. If they started charging for licenses I would still use it.
For what shall it profit a man, if he shall gain the whole world, and lose his own soul?