If I remember, cfb mentioned that you can forge with 2 or possibly more account from same running Nxt.
I wonder though, can one log in any node and close browser to be able to forge?
From what I understood the Account Control (is that the right name?) feature will allow you to allocate your "forging" rights to another account (although I don't think that the specifics have been disclosed yet).
So I don't think you would need to be "logged in" at all.