I love this coffee shop - it's what I imagine Madison should be. Mermaid is small, relaxed and slightly hipster. It's a great place to grab a coffee and sandwich, and chill for an hour or two doing homework. The menu is more exciting than typical coffee shops (sandwiches & soups feature Indian, Vietnamese and Caribbean touches).
I wish it was walking distance from campus, but then I fear it'd lose its charm and turn into an undergrad hangout. I'm happy to abide by its cash-only rules, since it adds good karma to the neighborhood. Yay, Mermaid!