While you can "blog" with Joomla! it's not really a blogging system. There are a few components for blogging that were made for Mambo, that may work in Joomla! I also think that there's someone working on a new blog component for Joomla!, but I can't remember who, nor how far along they are (in other words, I wouldn't count on it!).
For a multi-user blog, I would look very closely at B2Evolution (http://b2evolution.net ). It has the added advantage of being multi-language out of the box. Further, Predator is working (in his spare{!} time) on a bridge/integration between B2Evo and Joomla! (http://forum.joomla.org/index.php/topic,1360.0.html )
HTH
Is it true Predator ? Joomla!/vBridge/vBulletin/B2Evolution would be a powerful combo ! How about all in the same user base !

