Is tipping style related to type? I've noticed I'm kind of an emotionally generous tipper. About as low as I go is 20% (15% if they give bad service) and I've never stiffed anyone. That and I tend to give ridiculous tips for good service. The restaurant I just got back from my waittress asked if I wanted a dessert and gave it to me for free so BOOM 50% tip. It's kind of funny, but since I usually find a favorite restaurant to go to, after a while when I show up all the servers seem really happy to see me.
Also, I'm one of those people that draws smiley faces on the receipts.