Well, I did sympathize that the line does leave it open to interpretation, but my realization of Tobi being Madara actually came from the first spoiler pics w/o any translations. It just makes the most sense to me, since:

  1. There have been frequent references to the existence of a 3rd Uchiha
  2. Madara has been revered as the "ultimate Uchiha"
  3. The likelyhood of someone besides Kakashi having a sharingan implant seems very small.
  4. The likelyhood of a "false uchiha" having the strongest sharingan seems completely impractical.
  5. Obito would OBVIOUSLY not be the main villain.


Edit:
Nobody has confirmed that Madara was the 1st Hokage's friend.
Itachi's friend was Uchiha Shisui (sp?)