So here's my two cents
I'm with Morbug, I worked in a lot of restaurants while I was in school and after, and as a consequence I tend to tip pretty well. But I feel they need to earn it too, and don't automatically deserve it. I'm just pretty easy to please in that regard.
Sit down dinner it always 20% unless the service was bad (not the food), if there was attitude, etc.
Take out is a case by case basis. I usually throw in a buck. I know a fare share of restaurant workers/managers, and I feel compelled to tip just because I know what its like, and I'm picking up some slack for someone who didn't tip earlier when they should have. I don't expect everyone to, nor do I think its required in most cases. I can see why people have tip jars for take out. Some guy who splits the tip is still putting together a to-go order in place of an order of someone who may be sitting down for full service. Sure restaurants are set up for both take-out/sit down, but some people are doing the same work for either one. Again, I don't this is a requirement though. Maybe just a little token of appreciation if someone was prompt, helpful, etc, because we know how rare that can be.
I usually tip a buck even for a cup of coffee, if I sit down in the place.
Not all receipts have a tip line. It just depends.
Of course there are good reasons for not tipping. I really can't stand attitude, so that right is the deciding factor.
