Tipping
http://www.newyorker.com/talk/content/articles/050905ta_talk_surowiecki
Tipping is an odd thing. Fundamentally, the idea is to reward someone for good service. But we only tip certain kinds of people. Waiters at restaurants get tips, and boys who carry your luggage to your room at a hotel get tips. Why don't we tip the handiman who fixes our kitchen sink? Or the people working at the bike shop when you need a tune-up? Simply social convention, it seems. If you're interested in the history of tipping and some studies done on what affects how much people tip, check out the article. (Stolen from Justine Larbalestier.)