It is pretty easy to scratch.
I've had this phone for less than two weeks now and while I've no case nor a protector on, I do take a damn good care of my phones. Alone in the pocket, never EVER had it even saw the tip of a metal.
But as it is now, I've a small scratch on the screen, about half a centimeter big. And only really noticeable in sunlight but still, I can feel it when Im swiping through the screen and feel somewhat annoyed instantly. Still though, No way Im buying a screen protector, those things are even more annoying to handle than scratches IMO, my TPU case is one the way though.
A Paranoid Google Nexus 4
HTC Vivid on stock Rooted ICS
S-On (yeah I know..)
HTC Desire on Runny rom 6.1.1
Past: htc HD2 - Samsung Vibrant - htc Inspire - htc HD7 -Motorola Atrix - htc Sensation - Galaxy Tab 7" - Motorola Defy - HP Touchpad - htc Amaze - Nexus 7 - Viewsonic gTablet - Motorola Photon - Sony Xperia X10 - LG Nitro HD - Acer Iconia 7" - htc Rezound - Motorola Atrix HD - htc Flyer