My family's been in the restaurant business as long as I can remember so I always tend to overtip. Usually I'll tip about 40-50% and more if the service was good. But it all depends on how the server seems, because sometimes ya the service will be bad but it'll be so busy. As long as they're trying to get you to enjoy your meal I think they did their job. Free drinks and a few extra things like adding cheese for free always tend to make me tip alot more. Like when I goto IHOP on Roswell Rd, the guy named John always serves me, gives me great service and free drinks and to go drink cups, I end up always tipping 80-100% on the meal. The meal would be around $30 for my friends and I and I would usually leave around $20+.