Sometimes the people waiting on you have just undergone a *career change*. For right now, waiting tables may be the best they can get, and without knowing you personally, I'd bet that you would have contempt for somebody drawing unemployment who was offered a job and refused to take it because they thought it was "beneath them."
In this economy, I have to look at someone waiting tables as somebody who is at least trying. I don't eat out anywhere near as often as I used to, but when I do, I engage the server in some idle chit chat when they first introduce themselves. 90% of the time, you'll know at that point pretty much what kind of service you're going to receive and what kind of tip you're going to want to leave.
I pay for the service they give me, not for their life circumstances. If they want a good tip, they should earn it.