I saw a report the other day on the news about this. They were saying that there is a growing trend of people not tipping the usual 15%-20% because of the economy. People felt that they just couldn't afford to tip and that the restaurant is lucky to have gotten their business at all.
I don't understand that mindset, because to me, tipping is a part of going out to eat. It should be factored in and expected. Of course, if the service was horrible then I think anyone can understand tipping less the usual, but for anything else there should be a 'normal' tip left.
I think some people are just using the economy as an excuse to be cheap. How they could actually feel good about it is beyond me. If you can't afford to tip then you need to be doing take out or eating at a place where there are no waitresses.