I'm from PGH
The short answer is that is depends where you're living and where you're working. Most people who use public transit in pgh use the Port Authority (bus line); generally in the city proper Port Authority is pretty good. The T and the inclines are other options which aren't awful and can be useful to a certain extent depending on where you want to go.
Can you live without a car in Pittsburgh? Yes, more so than most other US cities, but only if you live in Lawrenceville, Oakland, Bloomfield, Shadyside, Squirrel Hill, Golden Triangle, North Side, South Side, etc. You'll need a bike as well. Keep in mind it gets 90F and sickly humid in the summer and 0F in the winter with constant snow, sleet, slush, frozen rain, whipping wind, etc. Additionally Pittsburgh gets a lot of rain in general, so keep that in mind for transit.
If you're coming from NYC or Chicago you'll hate it (we don't want you here anyway). If you're coming from Dallas or Atlanta or Denver it's much better.
