A List Of Things Thrown Five Minutes Ago

URBAN PROBLEMS DESK:It's been a few years since we last discussed it, but as we come to the end of the year, it's time to once again discuss the question of holiday gifts/tips.  Two questions:

1. Is a tip/gift a reward/incentive for past performance, or is it an encouragement for future performance?  For instance, I moved earlier this year into a new building.  Is a lower gift appropriate as a result? 
2. Who to give to and how much?  Some are easy--my assistant gets a gift, and the three doormen on staff at my building will each get something and a card, but mail carrier?  Newspaper delivery?

My inclination is $5-10/month lived in the building for the doormen (who address me by name and are constantly helpful), but I want to make sure I'm not out of the ballpark there.