I traveled to NYC for the weekend and wanted to try Megabus for the first time. I took the overnight (red-eye) bus both ways, and found it to go rather quickly for 8 hours each way. In Pittsburgh, the bus picks you up at the David Lawrence Convention Center. If you pay for a "reserved" seat, you get to board first. I'd recommend paying the extra $7 to pay for one of the front row seats on the second floor; you can recline pretty far and get a great view of the road. If you're tall, any seat will probably be pretty uncomfortable for 8 hours (think airplane space).
The only CON I had about my trip to NYC was the driver. Although he was initially experienced as firm but humorous with his expectations, he began being condescending and patronizing at each stop ("You are all adults, there should be no reason why you can't get back on the bus on time"). The driver from NYC to Pittsburgh was much more pleasant.
What I appreciated most about the bus ride was that they switch drivers halfway through the trip (I'm not sure if this is only for the red-eye), which made me feel safer. For the decent price, I'll probably take Megabus again.