Joomla is simply some of the best FOSS available.
I am an 'Average Joe C programmer' and have used Joomla to create at least 4 simple sites in under a weekend of work (including writing my own templates, and components).
My only complaint with Joomla has been that the CMS does not have automated way to download and install CMS/component/template/module updates (e.g. something like apt-get update/upgrade). Unless you keep on top of security patches your site is very likely to be cracked within a year in my experience. However, that said, if you keep on top of the updates the you're likely to save yourself a whack of work by using Joomla.
Joomla 1.0.x, and 1.5.x, have both been amazing and keep getting better IMOP! I look very forward to 1.6!!
Sorry I didn't tweet about Rex. He's embarrassingly frisky so I tend not to bring it up.