The S3 has Gorilla Glass II, which is stronger but also thinner than GG1.
I am pretty sure that the net effect is that it is weaker.
Also, the glass on the S3 goes very close to the edge of the phone, especially at the bottom - if you drop it and it lands on one of the bottom corners it WILL break.
Furthermore, Samsung saw fit to bond the LCD to the glass, meaning that if you do crack the outer GG layer, you are basically screwed.
Sammy told me that my warranty is invalid until the glass is replaced - ie if the device died and I sent it for repair, they would not repair it (Or even evaluate it) until the GG was replaced, at a cost of about £170.
Add to that the fact that I have a custom colour ("Amber Brown" from Phones4U) and Sammy say that they do not have that case colour, so in order to replace the glass/LCD assembly, they would also have to replace both covers as the front bezel is bonded to the glass.
Very annoying as there are a bunch of youtube vids that show how to separate the glass and LCD using a heatgun or a playing card, and you can get a replacement glass for £10 - obviously though this would invalidate the warranty.
So to replace a £10 part, I need to pay in excess of £200.