I've worked at Applebee's for almost two years, and when you're getting paid $2.13 an hour to wait tables, you survive on your tips. A lot of the people I work with are single parents, who support themselves and their children on the money customers leave on tables. Taking care of a $100 table and not getting a tip is like getting punched in the gut, and it's not fair. I tip based on the service I receive. If it sucks, so will the tip. If it's great, the tip reflects that as well. If the service is so bad that I don't want to tip at all, I'll usually get a manager involved before the ticket even comes.
I'm the type of person that believes that if you can't afford a 15% tip, don't eat at a restaurant that has servers.