Merav, i cant find you on my list. But i would be happy if you can update this articel that i found when google..
www.ijoomla.com/blog/one-set-of-joomla-users-multi… - I should be great if this artical can support Joomla 3.x .. Thanks!

One set of Joomla users, multiple Joomla installs » iJoomla Blog