If you are downtown, the two easiest shops to get to would be Probikes and Biketek both in Squirrel Hill both on Forbes Ave. I would suggest Big Bang Bikes also, but they are a little further out of town. Top of the line shop though. Dirty Harry's is another good shop, but even further outside of town. If you do find time to ride, Frick Park, off of Forbes Ave. is the easiest place to get to for trails.
^What he said. Frick park is right in town and has some great trails. Dirty Harry's is a little bit north of Pittsburgh and is in Verona, PA along the Allegheny River, it's a great shop but it's probably about 20 minutes away.
Get a bicycle. You will not regret it if you live. ~Mark Twain