I am with a lot that wish the whole tipping thing would go the European model where it is included in the price and you may leave an extra 1 or 2 Euro for exceptional service. This based on a percentage idea is stupid. There was a Chinese food restaurant I would go to with my family (4 people) for $40 and we would have enough left overs for a lunch the next day. Tipping a "generous" 20% after tax was $8. I go to a nice restaurant with just my wife, with a good bottle of wine and the pre-tax amount is $200. Tipping a "miserly" 15% pretax is $30. 
So for the same job for around the same amount of time my $8 tip is generous and the $30 tip is cheap? 
If the waiter at the nice restaurant has 3 or 4 tables they can be pulling in over $100 a hour in tips and a good portion of that is tax free.