Fair Trade is one of my favorite cafes to go to, mainly because they offer a nice selection of coffees, pastries and foods. In a pinch you could even have a semblance of lunch here, unlike Espresso or chain-y coffee places around. I recommend the spinach mushroom quiche.. :-)
I like the big window for people watching and the seating out front to sit at during the summer.. The people who work here are all nice and helpful, too.
Overall, while its not necessarily your most interesting coffee shop around, its a nice setting to get work done, camp out on your laptop (as I'm doing there right now), or just people-watch at one of the busier corners of State St.