at the moment preferences are shared between users, however the perception is not the same according to where you place the portlet.
In a portal site (like classic) : it is shared among all users that can use the portlet
In a group site (like /platform/users): it is shared among all users of this group
In a user site (like the root dashboard) : it is shared only for the root user (which means that it is personalized to him).
In JBoss Portal we had support for personalization per user in a shared context but not in GateIn. We do have plans to bring this behavior in GateIn 4.0 although it is not yet scheduled.
Thanks Julien for this quick reply.
It is important for my portlet project to be able to share the preferences, so this behaviour perfectly meets my needs! I was just afraid it could be considered as a bug for the future releases since it is not exactly what the JSR 286 specifies. Then finally all is right !