Just wanted to throw my two cents in there, as someone who has worked as a delivery guy when i was younger and also as a waiter at a reasonably classy establishment.
As a delivery guy, i don't think you should make anywhere near the tip that a waiter/waitress earns. And when i say earns, that's exactly the reason why. As a delivery guy, not only do you make a "delivery fee" for every order you take out (which is put in place to cover your gas money and is usually MORE than enough for that purpose) but you also do far less work. Generally you are delivering in a fairly small area that you know very well, and the rest of the time that you arn't out for delivery you are either helping do very small tasks back at the business or yucking it up with the guys you work with. (This was my experience anyway.. but it was far less work than waiting tables.) I generally leave them between 3 and 5 dollars and i think that's more than fair.
As a waiter, i am on my feet every night running around like a madman with no breaks and no stopping trying to please every single individual at my tables, and usually i am waiting on about 15 people at a time on average. That would seem to be a tremendous chore in itself considering how impolite alot of people can be nowadays and how most don't understand that there are other people besides themselves in the resturaunt at any given time. In addition to doing that however, whenever we do get a second to take a breath, we also have work to be done all night "sidework" that must get done in order for the resturaunt to function effectively. Such as restocking plates and glassware, filling up tea pitchers, ice, bread, etc..
..and on top of all this, whenever i get an extra second (somewhere in there, its hard to find haha) im helping others who are a little behind or "in the weeds" we call it and need a hand to make sure they don't upset their guests. Its really a crazy business and you need to be able to multitask and have a good head on your shoulders to profit. You also need to be in reasonably good shape.
Through all that, i'd say if your waiter/waitress gives you standard to good service then 20 percent should be the tip. If things went a little rocky and you were unhappy with a few things then i would say 10-15 percent is more than fair. If you were very happy with the service and felt your waiter/waitress did better than most then i would say 25 percent or more would be generous.
As far as what i leave, when im out i almost always leave over 20 percent for adequate to great service, just because i know how hard it can be sometimes.
Its really all up to the individual though.. i try to give every customer i have the same quality of service and my goal is always to know that for at least one part of their busy day, i facilitated them being able to relax and have an enjoyable experience. I try not to worry about what percentage i make off of each person, since i know there are different factors that go into a tip for everyone, but try to keep in mind how hard some of us work for you when you go to leave that tip at the end of the night.
