Although the Mattress Factory is literally on my street and I get free admission for being a grad student at Pitt, I've only visited once.
My friend and I stopped on a sunny afternoon, and toured both the main museum and the annex gallery. It was interesting, but definitely by no means the best museum experience I've ever had. I've heard the cafe is amazing, so if I go back I'll update this review accordingly.
My favorite piece was "My Offering," a room full of plaster hands holding Breadworks bread.
My least favorite was a dark room where you were supposed to sit until something appeared. We got so freaked out that they were watching us with a camera and were going to pop out haunted house style and scare the crap out of us. But then again, maybe that was the art...?