I've heard that one of the extra costs associated with cruises is tipping. How does it work? I'm used to tipping based on the price of items (15-20%), so if I'm not paying, I'm not sure how to know how much to tip.
I've seen some mention of an overall "gratuity" being included in your bill at the end of the cruise — but then I've also had friends say that you need lots of $1's for tipping around the boat.
So, which is correct, and/or how do I know what to expect on a specific cruise or cruise line?