1369 Coffeehouse on Massachusetts Avenue in Cambridge, MA (Central Square). Great atmosphere to sit and lounge while hanging out with grad students/[ex-]dot com entrepreneurs/artists/Cambridge intelligentsia/some combination of the preceding. It's nothing fancy, but the coffee is great, the staff is friendly and cares about how one likes his/her coffee and how their coffee tastes, and the baked goods aren't bad (and made on-site). I just about lived there through law school, up to 10-12 hours per week--and there were many who were there far more often.