Mine has scratched. Nothing major, just two very small scratches that you can't even see unless you tilt it just right under a bright light. But, they're still there.
It'll be fine as long as you keep the phone by itself in your pocket.
Sent from my Sony Xperia ZL
If I put the HTC One in my pocket on its own with nothing else in it, is there any risk it can scratch even small scratches? Like rubbing against cotton/denim?
the screen is pretty resistant if you take care of it as you appear to be doing. ive had mine for a few weeks without protection and the screen has no scratches...
the camera glass, however, is somewhat more prone to scratches. be careful where you rest your phone because the glass will be in direct contact with the surface. pitty htc didnt use sapphire crystal like apple did with the iPhone 5 for this purpose.