I am a CMU alumnus. Is he going for engineering? Tell him to be prepared to work hard, party hard and forget about finding a girlfriend.
Where are you guys coming from? Pittsburgh once attempted to market itself as "the city with a smile on its face." We are notorious for being friendly, or at least polite. People hold doors for each other and such. We like to give directions based on landmarks that aren't there anymore.
It's a "midwestern" city more than a northeast type. It's generally a low crime city, divided into unique neighborhoods, which still retain some vestigies of ethnic enclaves. The CMU campus borders a large city park and is pretty insular. Your son will have little need to leave the campus to do his day-to-day things, so it's not like he'll be in an urban atmosphere.
The University of Pittsburgh is right down the street, so when he does choose to explore the area, he's got all the benefits of a neighborhood that caters to college students, with record stores and fast food places and such. And of course the O, famous for its french fries.
SD
Take a left turn 1 mile before where Macaffeys barn used to be?