K Prime figured this out (i think).
http://www.youtube.com/watch?v=A3gO6w_5eyo
In short: When G&W UpBs to grab the ledge, there is a 1 frame vulnerability after G&W stops being invincible but before he grabs the ledge.
How does it affect you? It shouldn't really, though it would have if you didn't know about this. Having a 1 frame invulnerability window might be true but the opponent guessing when G&W will actually UpB is impossible. G&W has so many frames to wait and see what the opponent does. Them reacting in 14 frames (or less) is nearly impossible.
Also, G&W's sweetspot range is ridiculous!
http://www.youtube.com/watch?v=A3gO6w_5eyo
In short: When G&W UpBs to grab the ledge, there is a 1 frame vulnerability after G&W stops being invincible but before he grabs the ledge.
How does it affect you? It shouldn't really, though it would have if you didn't know about this. Having a 1 frame invulnerability window might be true but the opponent guessing when G&W will actually UpB is impossible. G&W has so many frames to wait and see what the opponent does. Them reacting in 14 frames (or less) is nearly impossible.
Also, G&W's sweetspot range is ridiculous!