You will hear both sides. Side A is: " I have had 20 iPhone's, kept all of them in my construction tool box and not one has ever even gotten the slightest scratch!". And Side B: " I walked out of the Apple Store with my new phone, gently wiped it with my 1200 thread count silk shirt and it got a scratch!".
It's up to you. I know too many people who have scratches from not dropping them, not banging them against things and who are careful, so I use a screen protector.