Well, it does get one from point A to point B in Pittsburgh.
But it's expensive, at least compared to the Metro Transit in Minneapolis that I'm used to. On Port Authority, it's $2.25 for a ticket, and an extra $1 for a transfer (which only gets you on one more bus, not all the way to your destination if it requires a bunch of transfers.) Coming from a maximum of $3 for two and a half hours of bus rides (express bus during rush hour), Port Authority is steep. I had to grab cash a couple of different times just to make sure I could keep paying fares throughout the days.
There's no day pass. Boo. If you're traveling a lot throughout the day, it adds up fast without some sort of pass.
Also, the 28X doesn't pick up passengers coming from downtown into Oakland (or drop them off in the reverse direction.) Very frustrating, especially with a Megabus terminal only three blocks away from one of the stops. (There's also Greyhound and Amtrak downtown, if I remember correctly.)