What is Joomla? “ Joomla is an award-winning content management system (CMS), which enables you to build Web sites and powerful online applications. Many aspects, including its ease-of-use and extensibility, have made Joomla the most popular Web site software available. Best of all, Joomla is an open source solution that is freely available to everyone.” ~ Joomla.org
Blogging requires some tweaking – Joomla! doesn’t have blogging functionality built into the core. You have to add extensions for comments, tagging, etc.
User Access Control – You can assign various levels of control, but you can’t specify sections of control. With so much control over organizing content, it would be nice to assign users to specific areas of the website.