I've always done the 15% tipping thing.I worked as a waitress and earned well the tips I made. But coming back to Oregon, I found they put everyone's tips in a jar or pot, and distribute and tax them at the day's end. So whether you do a fantastic job, or a crappy one, you reap the benefits of the good service workers. Not fair. If someone is outstanding, I will give them a personal tip; directly into their hand and tell them not to share. They have to divy up part of their tips to the cooks. Unless there's something WAY beyond exceptional that's been served, I figure the cook is being paid a lot more than the wait people anyway.
But that's just me.