There is now the ability to keep simultaneous logins. Thus, you can remain logged in your browser at home, work in a browser at work and on your iPhone at the same time, for example. iPhone regular Web site I am referring to, for now. But, all this should work, thus requiring a logout, as usual, if you really want to make sure you close one of those sessions.

So, this means if you log in from a secondary browser or device, you are not force to log in again from the first one. Then, of course, your session state is replicated across all sessions.