I can't speak for everywhere, since it varies so much, state to state. Here in North Carolina, the minimum wage is $7.25, and my two teens both work as baristas. One earns $15/hour plus tips (Starbucks), the other $10/hour plus tips (local chain). Mr. $10/hour gets his tips daily, and makes roughly $10/hour in tips. He also has to report them daily--it doesn't affect his wage, it's to make sure he pays the appropriate tax. Which, for him, will be $0--he won't earn enough to pay taxes. I actually think he brings home more in tips than his sister, but she gets them weekly. Since she's in college, I don't see her tips daily like I do her brother--he lives at home, and is always asking me to trade his tips for larger bills (I currently have $70 in $1 bills in my purse, until I get to the bank).
I'm in the camp of, if you get a simple order, no tip, or a small one, would be appropriate. OTOH, if you're ordering multiple drinks, or something complicated or off-menu, you should leave something. DD19 had a woman order a drink with 23 stevias in it yesterday (?!?). Exactly 23. Someone like that should tip! It was way more complicated than just that, DD mentioned it because the woman was talking to her while she was counting the 23 stevias.