From the conference’s website:
Third party developers are vital to the success of Joomla!. To be effective developing extensions they need up to date information about developments in the Joomla! core and how to work effectively and using best practices when extending it… The conference will include training targeted to experienced developers, information about Joomla! 1.6 and opportunities for networking with other developers and core developers.
Before you go running off to register, however, be sure to check that you "already have good working knowledge of Joomla! extension development and the Joomla API. [The conference] is appropriate for extension development firms, custom Joomla application developers, and in house Joomla development specialists."
If you want to attend, hurry to register as seats are filling fast. The event is $100 but some scholarships are available.