I always say thank you when someone opens a door for me. I also try hard to teach my two year old manners...and she is surprisingly good for a two year old. It's not just youth these days with no manners. Walking into the Doc's office the other day carrying my newborn in her carrier...the man in front of me opened the door for himself and his son and then let it close on me...hitting the carrier that my daughter was in! I loudly...but politely...said THANK YOU!! (He didn't even acknowledge me.)
I agree though...good manners can be seen in the majority of people I encounter in a day. It is the odd person who lacks decency that sticks in your head though.