I took the bus several times on a recent trip to Pittsburgh.
The 28X/"airport flyer" is a good option to get from PIT to the city--and at $3.75, probably $35(?) cheaper than a cab. The bus was also reliable in getting from my Oakland hotel to Downtown, and from Oakland to Regent Square--especially considering the dearth of cabs in the city. The regular fare of $2.50 is a bit steep for the shorter trips, and when to pay can be confusing (sometimes when you board, sometimes when you exit), but those are minor annoyances.
TIP: Download the Tiramisu app for real-time bus tracking. Worked great while I was there, and I loved that you could enter the time you got on the bus, so the app would adjust arrival times for future stops accordingly--terrific idea.