How Much to Tip?

As a customer, it's important to tip for good service. Lots of workers including waiters, bartenders, hotel concierges, and salon workers rely heavily on your gratuity, but we've fumbled over tipping for valet parking and coat check more often that we'd like to admit. Want to give the right amount without looking (gasp) ungenerous?  

And how much tipping is appropriate? After all, it's not your job to support your waiter's family, especially if you feel that a tip is undeserved.

Here are some g...