I have noticed that on some occasions, and this is easier to see on a board that is scarcely populated at a time, but when you are navigating through topics in some instances it will say a guest is viewing the last topic you viewed or rather that your last action is getting replicated by a guest. I also saw that Takuthehedgehog was capable of doing another action while the other two accounts just idled into oblivion. I'm aware that you cannot log in more than once on another machine though - it just updates with your new IP to the Who's Online list or your old one stays until the list itself is refreshed.