I had just moved to a new area, and got into the habit of taking myself to, of all places, IHoP once a week. It was nearby, not that expensive, and I could think and read and people watch. I would routinely tip 100%. It meant a lot to them but wasn't a lot of money.
I once tipped about 10% because I'd gotten comped a bit more than half my meal (a waitress spilled food all over my lap). I wasn't really paying attention when I paid the check and just tipped on what they asked me to pay. It wasn't until the next morning I realized the waitstaff had still done all the work of giving us all the food. So I looked up their menu online, figured out what the right percentage would be of what I'd been comped and went back to the restaurant. It was pretty funny trying to describe the waiter to the manager. "Um, he was a guy, he was wearing black pants, white shirt...."