Hey yo!
Lots of interesting conversations going. I would like to jump into the fray about whether Tobi = Madara or Obito??? My points should not be taken as support for one argument or the other, just interesting observations that show why we really can't be sure who Tobi may be, and here is why:
1. I believe the latest time period in which Tobi was introduced was during Naruto's birth, ch. 500 pg. 14. Because of Tobi's mask we can't be sure of how old he is. Since Obito was around Kakashi's age we can expect Tobi, if he is Obito to be a close to the size of a fully grown man, since Kakashi is such during the events of these chapters, ch. 502 pg. 2 we can dismiss the common issue with Tobi, If Obito being too young for him to portray Tobi during this time.
2. Yes, Obito did give his LEFT eye to Kakashi, so people ask how can Tobi, If Obito have two eyes as shown in his fight with Konan? ch. 510 pg. 8. Well, Tobi seems to have a supply of Uchiha sharingan, ch. 482 pg. 13 (See drawer with sharingan, then see many more drawers). I know to obtain EMS an Uchiha needs a siblings sharingan, but we have not been informed that any uchiha's sharingan can not replace a fellow uchiha's lost sharingan. Moreover, an MS is required in order to do special ninjustus like: susanoo, amaterasu, and Kamui. Kamui is a similar space-time ninjustu, similar to what Tobi uses. We have never seen Tobi's right eye when he executes his space-time ninjustu, thus we don't know what is MS looks like...could it look like Kakashi's MS? This would provide us with an answer to how a non-uchiha like Kakashi could achtivate a MS, meaning once Obito activated his MS (if he is still alive and acting as Tobi) it in turned activated his other eye, which Kakashi has. Furthermore, Tobi could sacrifice his left eye by using izanagi during his fight with Konan, ch. 510 pg. 10, because it is not an MS unlike his right eye, which is very key to his effectiveness in battles.
3. Tobi claims to have obtained Hashirama's powers during their fight. How could Tobi, if Obito possibly have obtained his powers, since Hashirama was well before Obito's time? Well, Danzo proved to us that Hashirama's powers can be obtained and used in ch. 478 pg. 11, because the first's DNA is still floating around somewhere, probably in the deceased Oro's lab, ch. 478 pg. 10 (see bottom left hand frame when Tobi is speaking).
4. Tobi could be Madara as well. Tobi, if Madara could have used his space-time ninjutsu to bypass the laws of time and not age as rapidly as the people in his generation and future generation, while putting all the pieces in place like he has done thus far.
5. If Tobi really is Obito we can conclude who is in the mystery coffin, ch. 490 pg. 4...Madara. Tobi seems to have a secret that Kabuto and only he know. Could it be that Tobi is lying about being Madara, and is really Obito, while the real Madara is a pawn of Kabutos? We will see.
6. Whomever Tobi really is Zetsu had an important hand in helping him arrive to the destination he is currently at. These are perfect words to describe the relationship of Zetsu and Tobi, ch. 487 pg. 1. I'm excited to learn more about Zetsu!
Sorry if this is hard to follow. I know it is very dense because of all the info. If you wish to see my references just go to the given chapter and page. For some reason I am unable to post the link. I'm not sold on Tobi being Obito or Madara yet, but he is a great antagonist! Farewell fellow nin!