Something I wished to point out in the tobi isnt madara debate.
Here is narutos bijuu seal when the kyuubi has its way (the twirling pattern)http://www.onemanga.com/Naruto/439/11/
Now notice tobis mask as well as MS pattern.http://www.onemanga.com/Naruto/475/10/
And the fact that whats in there is another deminsionhttp://www.onemanga.com/Naruto/475/15/
kind of likehttp://www.onemanga.com/Naruto/439/11/
Granted Im not sure how other people can be pulled into that demision, ect. Ill just work on that later.
So the SG Tobis using is the seal, his body is compeletly fake, and the beast that should be inside is gone.
Conclusion: Tobi really is some kind of bijuu (juubi or yin kyuubi chakra) that exists completely through that one eye. but with all other evidence such as.
1. the power of the SG and the juubi do seem to be connected, not the SG and the RG.
2. Tobi has one powerful eye and so does the juubi. Could be an obvious reveal of tobis true idenity by kishi.
I think its more likly that tobi=juubi not yin half of kyuubi.