Im still pretty sure it goes something like

1st user - long dead member of the Uchiha clan. Made the scrolls with the info on how he obtained.
2nd user - Itachi (whos already greatly gifted) finds the hidden scroll, kills his homey, gets Mangekyou Sharingan. A short time afterwards and with his family finding out or on the verge of finding out goes mad and kills everyone but Sasuake.

About 10 yrs later or whatever - Sasuake and Naruto have their Battle but Sasuake is unable to kill Naruto.

-Anime hasnt had these parts yet so i may be wrong-

A short time after - Kakashi learns Mangekyou Sharingan to the surprise of.. well everyone