As others have said, it's crazy that you can review "a hill". However, Flagstaff Hill really is a great place to hang in the nice weather.
Lots of grass games and picnics happen here. Plus, the sunbathers usually are wearing an appropriate amount of clothing compared to some of the things I've seen in other parts of Schenley Park recently. Of course, in general, CMU students wear more clothing than Pitt students so choose your locations accordingly.
The parks dept shows movies here during the summer, and the view is spectacular...nestled between Phipps and CMU with views of the city...it's almost perfection! On weeknight movies they even have bands play! For movie information go to: http://pittsburghpa.gov/citiparks/cinema-in-park
The best part is that if you need modern conveniences--read: bathrooms--the CMU buildings are right there! Plus, there are food options as well although less things are open during the summer.