Tim Harford, Slate's "Undercover Economist," reports on research by economist Caitlin Knowles, who studied waiting times of different groups at eight coffee shops in the Boston area. One of the more robust findings was that women have to wait longer to receive their orders. This effect persisted even after controlling for the type of drink ordered. And, it did not appear to be a case of employees trying to flirt with female customers, as wait times increased when the shops were busiest (when you would think flirting is least likely to occur).
The results are a bit curious because many economists think that competition should reduce discriminatory practices. A discriminatory coffee shop is driving away customers and the associated revenues, which is not likely sustainable in a competitive environment.