I'll usually tip 20-30% but sometimes more if I'm in a generous mood, and usually more at breakfast which is so inexpensive; I feel sorry for the breakfast shift waitstaff! If I get truly bad service, I'll leave a note explaining why I left no money, but that's very rare. The last time I remember doing so , was because I waited for 30 minutes to have my order taken, and another 30 for my food, during which the waitress never came back to check on me. I never got my drink or salad, but after she finally brought my food I never saw her again. I had to ask the busboy to get my check! (And I did tip him a buck- he was back in a flash!) This was not in a cheapo place either; it was about like an Outback or Longhorn. And it was very busy, but the next section was getting excellent service- too bad I wasn't over there!