Has it ever occurred to anyone that the Kakashi Gaiden arc has an important significance besides friendship being the moral to the story and the origin of Kakashi's Sharingan? In manga everything has to be incorporated some way into the plot and have a point. Very rarely you'll ever get a filler that's pointless. And sure Kishimoto may be that one mangaka who's done something different by creating a filler that really has no role to the plot, but I seriously doubt that because even he has to follow the guidelines. His editor wouldn't allow it. Manga fillers just don't happen.
Kishimoto needed to introduce Obito in order for the readers to know who he is because he will have a larger role in Shippuden sooner or later. That's the real reason for the Kakashi Gaiden arc. You may say the true purpose was to only introduce Obito to show how much he impacted Kakashi, but that's your opinion. Kakashi could have easily explained where he got his Sharingan from instead of going into an elaborate story taking place years before the current timeline. Why did Kishimoto choose to create an arc specifically for this detail just to past the time until the Shippuden manga started? He easily could have done something else.
Now there is this Tobi factor to consider. The similarities are uncanny.
Tobi and Obito's hair is somewhat of a proof to show they're the same person, but then again it's not solid evidence since spiky hair is one of the more common hairst*le inn the manga.
Then there are their personalities. They both seem to have similar ones like being carefree and slightly cowardice.
What about their names? T-O-B-I? O-B-I-T-O? Looks like an anagram...
What about Tobi's mask? Sure, any random person can wear a mask, but a mask with only one eye hole? That's unlikely, especially if the eye hole just so randomly happens to be the hole for the eye Obito still would have had. Coincidence much? It's also unlikely that the eye Tobi has hidden is still there because it is rather stupid to have a mask with only one hole if you have two perfectly good eyes.
If that doesn't convince you guys, then what about the little fact that Tobi has a SHARINGAN. If that doesn't set off any bells then I don't know what else to say other then there's seriously a large case of denial running around because no one wants to admit they may be wrong. If you think Tobi is some random Uchiha then Itachireally did a poor job with the extermination of his clan if a ninja of his caliber missed one person unintentionally. If you think Tobi is Madarain disguise solely because of the famous line in the manga where he says "My power... Uchiha Madara's power.", then I hate to break it to you but the Sharingan is technically Madara's true power since he did create it. Madara is dead. Although there is the possibility that Madara is possessing Obito's body. In my opinion, that's the most likely scenario.
But hey, I could be wrong. Kishimoto could be mind f**king us all with these planted details and come up with something really twisted and unexpected as the outcome to the Tobi enigma. Tobi could really not be Obito.But I don't see any solid evidence to prove otherwise. And don't say that Obito died is proof because Obito was still alive when Kakashi and Rin left him, and they never mention recovering the body. Plus people have a bad habit of never staying dead the first time in the Naruto world... There's just too many coincidences here to not be ignored just like how it was a HUGE coincidence the Yondaime Hokage "randomly" happened to look like Naruto.
If I'm wrong, I'll announce it for the entire world to see in big bold letters and italics AND say SasuNaru has no chance of ever happening... It means that much... but Sasuke's still gay 
Edited on 11/26/2007 1:23pm