Well what do people who can't afford to give extra do? Right now I'm on a razor thin budget and can't afford to tip people as much as I'd like to. Also, I wish I still used my debit card so I'm not given the eye at a certain coffee shop that has 'tip cups'.
Then you do what you can. I'm not going to preach at you, but I've always looked at the tip as part of the cost of the meal, just as the tax is. I've been in the same situation that you speak of: I was out of work for 4 months, so the only times I ate out were at places where there wasn't tipping (fast food or deli), and there was usually a coupon involved. I'm still putting my finances back together, but when I take a friend and his wife out to dinner (in return for doing the same for me when I was unemployed), I'll be making sure that I've got enough for the entire meal, including tax and tip.
I'm also not saying that you HAVE to leave a tip of a certain percentage. It's up to you to decide what the proper amount is: According to "them," the "proper" tip for good service is 15%. But what you leave is up to you. If you've gotten poor service, then you should leave less, and if possible, be sure to let your server know why they're getting less than they might expect, or even nothing. If you get really exemplary service, then leave more, if you can afford it.
Mark