PS3 will never overtake 360 this gen. Too late now. Way too far behind. Jpn have 2 million more PS3 but Americans have over 8 million 360s.
But if the 360 stops getting any decent games than it probably would overtake it in a few years. Or it might overtake in it's twilight years in which case the next gen would've already been announced and it wouldn't matter by then so fail.