Gorilla glass is on 240 devices across 24 major brands. Source: http://www.corning.com/gorillaglass/devices.aspx
Also, my Samsung Galaxy S has gorilla glass, but nowhere does it mention that in the manual or specs either.
But, unfortunately, the X10 does NOT have Gorilla Glass, it has toughened glass. This is based on the fact that there are a ton of websites which say it doesn't have gorilla glass, and none that I could find that say it does. There are also a number of comparison reviews that list phones it's comparing it to as having Gorilla Glass and the X10 as not. Also Gorilla Glass wasn't on any device until October 2009, and the specs of the X10 was decided some time before that.
In a way this was unfortunate for Sony, as the delays Sony suffered with this device meant that it had some major features that were considerably obsolete by the time it first appeared in March 2010. For example it shipped with Android 1.6, but phones had been running 2.0 since October the previous year, and 2.1 since January of 2010. It's only just got 2.1 when phones have been running 2.2 since May. The screen could have been the biggest on any Android phone, but it was beaten by several others (Galaxy S and variants, HTC Evo, etc), and also at a time when heavily customised UIs were becoming unfashionable due to update delays. I would have bought it when I first heard about it 18 months ago, but it just took too long
