I tip based on service. I don't care if they only make $2 hr base pay, if they don't earn enough tips to make minimum, the company has to match it.
The JOB they do is SERVICE, if they don't do their job, they don't get the money. It's that simple for me.
That being said, I have worked in the restaurant industry for several years when I was in college, so I know what it's like. I know a lot of people pulled in 2-3 hundred each night - so it's not like they are barely scaping by. That's not bad for a couple hours of work.