Will riding cobblestones and rough streets kill my cup and cone hubs?
Bearings and races are made of very hard steel. So long as they are properly maintained (lubricated and adjusted to the correct tightness; visit Free Ride in Pittsburgh for help lubing/adjusting your bike if it's feeling worn and you don't want to pay a shop to do it for you), they should hold up with no problem. 

More info:
http://en.wikipedia.org/wiki/Rolling_element_bearing