This event is scheduled to be held in November 16th to 18th this year in San Jose, CA, USA. You can purchase tickets, plan your travel, look for hotels and get information about speakers and talks from this site.
Last year the Joomla! community organized over 30 events all over the world, and had over 1000 people turning out in each. However, this is the first Joomla! World Conference. The conference will cover topics ranging from website building with Joomla!, managing the CMS to almost every aspect of this open-source CMS.
Joomla! had been powering websites since 2005 and some of the most popular websites in the world like Hardward University, Linux.com, etc run on Joomla! It's flexibility, ease of use and extensibility is incomparable to other CMS. You can see a demo of Joomla! from this link.