The old is it, or is it not Gorilla Glass debate.
I asked HTC if they were going to use GG on the Thunderbolt and got this:
@KingChicago We previously used GG. Since other damage-resistant glass tech has become available, we now source from multiple manufacturers.
However, at
Corning's site they claim the Tbolt has it.
Regardless, any screen can scratch, even GG. So if you have a tendency to do so, get a protector. I do not use one, just because I make sure not to keep keys in the same pocket as my phone, and have never had a problem. Its all based on how you use it, and how careful you are.