now now, i've been in this thread since v5 and i tell you many ppl have had their screen scratched    same case with casing too
yes, corning gorilla glass is hard to scratch, but not scratch proof, the hardest material to scratch is diamond, which is why its used as a drill bit. btw hard to scratch doesnt mean it cant be broken. remember previous science lession, harder to scratch = harder = less ductile = brittle = easier to break

let me put some facts straight since i've actually studied geology here...

first we have the Moh's Scale(you can wiki it)
based on http://en.wikipedia.org/wiki/Gorilla_Glass , gorilla class is at approximately 9 in moh's scale.

so ANYTHING MORE THAN 9 WILL SCRATCH IT

so here's an example of minerals more than 9

9-9.5  corundum, silicon carbide (carborundum), tungsten carbide, titanium carbide, stishovite
9.5–10  rhenium diboride, tantalum carbide, titanium diboride, boron nitride, boron.
10  diamond
>10  nanocrystalline diamond (hyperdiamond, ultrahard fullerite)

sure its harder than glass, and most of of the common metals, but do you know what are the sands made of? you'll regret it if your screen start getting microscratches