we usually ended up tipping on our bar bill at dinner and then leaving a little extra cash at other meals. we had some great service and it felt like the right thing to do.
One thing to be aware of is that when you order something and pay out of pocket, most places have already added an 18% tip to it when you get the bill. So watch that you don't end up tipping 36% on that glass of wine (unless that is your intention).
I tipped extra once to a CM I will never forget at Sci Fi. My DD was 6 months old at the time and I just couldn't console her- I was ready to walk out of the restaurant and just get my burger boxed up. Instead, he brought our food, and took DD from me and walked her around the entire restaurant so I could eat in peace. I will never forget that, and left some extra money.