Will poll workers ask that you show ID? Yes. Must you? In most cases, no.
UNDERSTANDING THE VOTER ID RULES – Most Pennsylvania voters will not be required by poll workers to present a photo ID when they go to the polls Tuesday (Nov. 6), the Philadelphia Committee of Seventy reports … although someone working the polls is required to ask to see photo ID, just as they were during the spring primaries. The part of Pennsylvania law that required voters to present a photo ID at the polls has been blocked by judges from going into effect for this election. Voters, however, could still be required to show a photo ID in 2013. That issue will be battled down the road, starting with a court hearing in December (2012).
Graphic from the Philadelphia Committee of Seventy