Wow, when I was a waitress at a normal restaurant, I only made $2.13 an hour, which is standard for waitstaff. We depended on tips too, and people sometimes wouldn't bother, even though we took the orders, brought the food, checked up on everyone, and cleaned up afterward.
I always tip my server at a normal restaurant 20% of the bill, but at a buffet, it really depends on the server. Some buffets I've been to, I wasn't even aware I had a server, because he/she never came around, so I left no tip. Other times, I've had wonderful service and left a full 20%.