I have done a fair amount of training and instruction of late on Jooma! (that exclamation point is part of the official name – damn annoying really). I continue to find it a very worthwhile content management system (CMS) with great extensions and flexibility. While I find it easy to use, teaching new users how to work with it always highlights for me the things that are not consistent in the UI and what concepts are tough to grasp for people unfamiliar with dynamic websites.
Frank Nilsen has done the Joomla community a huge favor by writing his “Basics of Joomla” book. It’s worth the small donation fee he requests many times over. The writing is pared down to be only what is needed to manage content, not build your own CMS, program Joomla or do any other gazillions of things that web developers would dive into but their clients would run from. So many of the help books are written for developers and not the “average” user who is someone with absolutely no web development skills. If you’re looking for a way of learning Joomla or need to teach your clients how to work with this tool, I suggest you point them to Frank’s website first.