Depends on what kind of song it is. If it´s some 3-5 chord pop song, I would listen it through once and be abel to play it. But if it´s a Dream Theater song, maby after 100 times but probably never.

Hav anybody tried that 16-notes lead from Dream theater´s Beyond This Life (it goes on the main riff at the tempo around 170) Man, that´s wicked.