Some of my thoughts on tipping:
People with kids should tip more. Kids' meals are cheaper, but they usually require more attention and more clean up. Plus, wait staff should get something for telling you your kids are cute.
I start my estimate at 20% of the bill BEFORE TAX, and round up or down from there, depending on the level of service.
I usually tip a little more if someone is drinking water, or getting constant free refills of soda. That's extra work for the staff that doesn't show up on the bill.
Call me cheap, but I tend to round down on the tip if folks are ordering the most expensive items on the menu. It doesn't take any more work to deliver a filet mignon than it does to deliver a bowl of spaghetti. I wouldn't make a major adjustment, just something minor.
If I am very displeased with the service, I will leave a minimal tip, just to make it clear it is deliberate and not an oversight. I always let management know if there is a serious problem with the service.
"It does me no injury for my neighbour to say there are 20 gods or no god. It neither picks my pocket, nor breaks my leg."
-- Thomas Jefferson