I find that the glass used on current high-end smartphones is pretty scratch-resistant. I am never really all that careful and have put them in my pocket together with keys, coins etc. My Galaxy S3 is essentially scratch free, and my 4 year old (?) HTC Desire has only minimal barely visible scratches, even though the rest of the coating around the phone is pretty much all worn off.
What I am really interested in is a material that will not shatter when dropped. This is the main problem with these thin phones with huge screens. We all know at least one person who is walking around with a cracked screen on their phone.