Big Dog Coffee serves Intelligentsia, like 21st Street Coffee, and though they don't have a Clover machine to make cups individually, it's still delicious.
The interior is a funky mix of bright pastels and European style paneling and wood; a coworker doesn't like it, but I do, so your mileage may vary. The interior has 2 rooms, and a nice layout that gives each table a different vantage point.
The pastries are tasty (from the samples I've had), though a little pricey for the size. They often have homemade or farmers' market goods, and the pastry stock appears to rotate.
A nice place to sit and study - possibly a bit better for that than for conversation, as the acoustics don't lend themselves well to private discussions (though I've never been there when the place was full, so more ambient sound may help).
For great coffee and atmosphere, this is one of Pittsburgh's very best.