I was full caseless and screen protector less with my X, dropped it a couple times on the corners, no glass cracked. I'm on the Sprint upgrade program and they only care that it can turn on and the glass isn't cracked. For my X Max I am using a GelaSkins skin because I like the designs, screen protector and a bumper. Bumper is only to keep the skin from getting caught on my pockets.
I'm a Marine and I took my X with me to the field all the time, put it in my flak, set it down on the ground, a few drunken nights out in Japan and my phone survived. All my Marines had cases and screen protectors and their phones, no matter Apple or Android, were always broken.
Everyone thought I was crazy to not have a case or anything. If it broke, it broke and I would fix it if it did. I'm an electronics tech and have plenty of equipment at my disposal to fix a broken screen if need be.