I spend a lot of time in coffee shops. Let me clarify this, I spend the majority of the time that I'm not at work or sleeping hanging about in coffee shops. One of the first things I do when visiting a new city is seek out the local coffee house, I feel these establishments are a great indication of the type of gritty art/music scenes I enjoy submerging myself in.
Pittsburgh has it's share of commercial, chain, and small/independent coffee shops. The Beehive has long since been one of my favorites. Located in the middle of the full on pandemonium of the Southside and East Carson Street, this place is constantly a hub of activity.
It specializes in more than just (hot & cold) coffee drinks, they also offer an array of breakfast/lunch/dessert food items too. The prices are low compared to most chains and while they only take cash they do have an ATM on premises.
Multiple rooms make it big enough to find a spot to sit with friends to talk or just grab a seat to read/write/sketch. This is one of my absolute favorite places to go for an afternoon/evening.