I think Orochimaru has either found out alot about the truth behind Tobi/Madara or has some so far unheard of knowledge of Rikudo Senin he came by on his quest for knowledge, or maybe even both - I think there are too many inconsistencies with Tobi BEING Oro, however, it is possible Orochimaru was involved in either creating Tobi's body or maintaining it during his Akatsuki time and that might also be why he knows so much - though if that were the case Tobi ought to have come after him to silence him. We lack the info but it sure is getting interesting again, and I'm gonna go on a limb and get down from my high horse of bitchiness and state that with Oro coming back there might be very good reasons for the whole Kabuto shebang I didn't like much so far. Hiro doing well I say
