We leave 20% for excellent service, 15% for adequate, and 10% for anything else. We never leave nothing because almost all servers these days "tip out" to the kitchen, hostess, etc., and those tips are usually calculated on the foods bills, not on what is actually recieved as tips. We don't feel it's fair that they have ot actually pay to be at work, so we leave 10%, then we talk to the manager.
At many places, servers end up getting to keep less than half their tips, and get paid just a few dollars an hour.
"This isn't life in the fast lane, it's life in oncomming traffic." -Terry Pratchett