I've been to Carnegie Mellon and it is right next door to Pitt if I remember correctly. I didn't see any poor neighborhoods around those universities, but I was only there for a weekend and this was about 7 or 8 years ago. We stayed in a hotel near Pitt and it was not anything luxury but I didn't think the neighborhood was comparable to N.Philly.

There are always town-gown problems in cities, especially if they aren't paying taxes on their buildings, which many do not. I think some universities have a better time of it because of the perception of the community, and that sometimes has more to do with what kind of respect university administration and leadership show to the community rather than if they are actually doing anything to benefit or harm.