If I launch a Joomla! 3 site, will I be able to install extensions?
From Joomla! Documentation
Revision as of 06:41, 28 September 2012 by Tom Hutchison
Yes, you will be able to install extensions compatible with Joomla 3.0. The Joomla Extension Directory (JED) will have Joomla 3.0 compatible icons to know which extensions are Joomla 3.0 compatible; however, the best place to check is the developer’s site.