I totally agree with Sapna about the Starbucks by the University Bookstore. It has both the worst service and the most expensive coffee on campus by far. In fact, there are some drinks on the starbucks menu that they don't even serve!!! When I want a passion tea lemonade, I don't want to have to walk all the way to brentwood to get it (this was two summers ago, mind you).
There is a reason for the overall crappiness of this Starbucks! And that is... dun dun dun... It isn't really Starbucks! It's a franchise that is owned and operated by Chartwells, the group in charge of food services on campus. And really, if you have any experience with U of C and Chartwells, it comes as no surprise. But that is the reason why said Starbucks does not take interac, credit cards or starbucks cards, and is also why they have painfully slow service and not much selection.