Are you guys aware that wiaters and waitresses make $2.10 per hour? That is well below the minimum wage. This is legal because it is assumed that these employees will make up at least the difference between their hourly wage and the minimum wage in tips. Busboys and bartenders are compensated similarly. Because of this pay scale, gratuities are expected by this type of service employee. If you fail to tip a waitress, don't be supprised if she spits in your omelette the next time she serves you.
I almost always tip service employees generously because I know that they are not paid a decent living wage by their employer. The only exception is a case where I am treated badly by a waiter. When this happens I withold the tip, but I also make a point of communicating the reason to the restaurant manager so the waiter understands exactly why he is not getting a tip. Then I make a point of staying away from that restaurant long enough for the staff to turn over. (See the last line of paragraph 1.)
Restaurant managers, on the other hand, are compensated well about the legal minimum wage. In fact, in some establishments, these individuals are not allowed to accept gratuities. I don't see any reason to tip them, unless it is necessary to offer a bribe to get a table.