I have read (and I can't remember where so don't quote me on this) that stretch marks aren't actually in the top layer of skin, so therefore anything you put on them externally isn't going to make any difference.
I had wicked stretch marks after Maya but they faded to the point where the lady doing my U/S with the twins commented how lucky I am not to have any. And I was way too lazy to put anything on them.
Oh and as soon as the u/s lady said that, I started getting lovely new purple stripes, so now I have another complete set