Did you know that in Australia or mainland China tipping is not customary? Leave your change on the table in Shanghai, and your waiter will likely chase you down. In America, tipping is everywhere and it can often get a tad confusing, but a gentleman always takes care of those who take care of him. Here are some simple gratuity guidelines.
20% is standard for good service. 15% for adequate. Even for horrible service, don't stiff them—many tips are split between busboys and bartenders, etc. (And unless you order a $200 bottle of wine, you should include drinks into your table's total.)
Depending on the bar, the adage "a buck a beer" will likely work. If you're ordering pricey cocktails, $2 (per drink) and the change will ensure that you'll be served promptly again.
10% of total bill (unless there's a delivery charge, then no tip is required).
15% of the total bill is standard.
$2 to $10 a night, depending on the price of the room and how messy you leave it.
$2 a bag for each bag brought up to your room or held in storage.
Asking for directions? On the house. Great seats for the show or a booth at the restaurant in town? A ten-spot is in order.
Can't do the math? There's an app for that. "CheckPlease" tip calculator for the iPhone, free at iTunes.