The day it's leaked is the day I abandon the interwebs and sweet tube-candy within.
Let me think... I was here for the 'unveiling' of the entire roster back in the Melee days... hrm...
I believe around a week or so around the release date in Japan is when the full roster started popping up. Of course no one believed it at that point (lots of, "Who the heck is Martha?" and "Mr.Game and Whatnow?") and of course NO ONE believed Mewtwo would be playable...
Then we got some screenshots of Ganondorf and Dr.Mario, which many people thought were fake... someone kept going on about giving the characters specific 'tag' names and then he'd believe him... also lots of whining about, "Ganondorf looks like he's going through the platform, that shot can't be real!"
Within a week of that event, someone managed to snag access to the IGN exclusive movies that were just coming out, showing the hidden characters and stages.