If you begin to have an IS consisting of N satellites sites sharing the same main domain, know that it's easy in PHP to share the session between all vhosts of the same main domain.
// Forcing registration of PHPSESSID's cookie on the domain of higher level ini_set("session.cookie_domain",".wandi.fr"); session_start();
Attention, last releases of Debian blocks this directive by default for security reasons. To enable it, add the following lines to php.ini (don't forget a small Apache restart):
suhosin.session.cryptua = off suhosin.session.cryptdocroot = off