Lived in Shadyside for the year. I loved the convenience to the hospitals of Oakland, the amount of restaurants in walking distance, the pretty tree lined streets, and the nice neighborhood bar scene. But, it was too quiet a neighborhood for me.
I'm moving away soon, after internship, but if I was staying I'd DEFINITELY move to the South Side. It just has more energy, diversity, and vibrance. Shadyside is nice, but unless it's Saturday afternoon and sunny, you won't see people out and about on Walnut (and on those sunny Saturdays, it's 28-35 year old couples with strollers). Southside has restaurants, bars, clubs, clothing stores, a great cineplex, chain stuff for the unoriginal (Cheesecake Factory, Urban Outfitters, etc.), and boutiques and vintages stores. If you're single and under 30, that's the place to be in Pittsburgh.
Later,
S