[Nexus S Q&A, Help & Troubleshooting] big_adventure:
I've had my NS for over a month. It has never seen a case. It's been in pants with keys, in pants with an un-cased iPhone 4, in pants with change, in jackets with keys and change, in a courrier bag with keys, change, a sharp metal mini-hard drive enclosure and dropped onto pavement a few times. The screen is absolutely scratch free.

There is a TINY bit of visible wear on the plastic back - especially at the very top and the very bottom, which are the leading edges when inserting and withdrawing it from a pocket.

One thing that has not been extensively examined so far - the "contour" display on the NS puts the entire face under more compression load when static, meaning that it will be MUCH harder to fracture, and therefore scratch, for a given strength of glass, since compression is where glass is strong.

Also, here is a little lesson on Gorilla Glass and any hardened glass. They are chemically treated to better resist surface flaws by creating compression in the surface of the glass. For Gorilla Glass, Corning starts with already-more-durable alumosilicate glass, and then uses their proprietary treatment it to better resist surface fracturing by penetrating more deeply than "traditional" glass hardening treatments on soda-lime glass - this means that, while you can still scratch it, the glass won't fracture as much around the contact, so you won't be able to see it as much. All of this is available on Corning's website.

For points of reference, here are my last 4 phones, their relative abuse states and what I saw out of them:

NS - one month+, hard use including travel, abuse my 2 and 3 year old kids, my daily high-speed bike commute over cobbled parisien streets, etc. Zero screen scratches. Oleophobic treatment seems to be holding up better than Apple's examples.

iPhone 4 - 4 months hard use as a phone, 2 more moderate use as a super-duper high-end iPod touch. Several very tiny scratches on the screen, and numerous tiny scratches on the back, then the screen shattered in the pocket of my jeans alone sometime on a transatlantic flight. I replaced the front and back with the "acquired" real Apple iPhone 4 white components someone stole out of Shenzen and sold through a site in NYC. One month light iPod use since, no marks.

N1 - 5 months as primary phone, then a 4 month break, then almost 2 more months as a phone when, battery be damned, I could no longer support the crappy mail and chat on the iPhone 4. It suffered very heavy use and abuse, including NUMEROUS hard drops and falls onto pavement and stone thanks to kids. The metal frame around the screen is VERY beaten up, and the edge has even cracked slightly on the screen from the compression around the metal edge, but the screen itself has no scratches.

Milestone (euro version of the Droid, complete with Gorilla Glass) - primary phone for about 3 months, and it had a long scratch down the face less than a month after buying it. But in this case, I know EXACTLY when it happened. It was in my wife's jacket pocket, and she gored it with diamond ring.

Finally, I don't think that anyone really KNOWS what glass is used in the Nexus S except for Samsung (and their provider, if there is one). I know that the Galaxy S, Epic, Vibrant, Continium, Captivate, and many other Samsung phones do use Corning's baby. I also know that many other products use it without mentioning it. I know that the iPhone claims not to, but that it does use some specially-treated alumosilicate glass.