Here is a breakdown of the petition challenges in Allegheny County races. I have spoken out about petition challenges before. I think in general they are undemocratic and are usually based on technicalities of the circulators, notaries, or signers that fill out their address/name incorrectly. It is an insult to those that sign the petitions trying to get candidates on the ballot.
See the whole list here: 2012 Petition Objections
12th District: The Mark Critz campaign is challenging Jason Altmire's petitions.
PA State House:
2oth District: The petitions of David Schuilenburg (Dem) are being challenged. The challenger's name is Robert Wilson and is the father of 2011 city council candidate Bobby Wilson. It appears to be the work of the Purcell campaign. Purcell has gone after candidates' petitions in the past.
22nd District: The petitions of Stephanie Crossey (Dem) and Shawn Lunny (Dem) are being challenged. Sources tell me that this is the Molchany campaign trying to setup a 1 on 1 race between her and Martin Schmotzer.
24th District: The petitions of Rep. Joe Preston (Dem), William Anderson (Dem), and Todd Koger (Dem) are being challenged. Looks like the Ed Gainey campaign is putting on a full court press.
33rd District: I read the Department of State's petition challenge incorrectly and thought that someone was running in the 33rd District for State House, but it was actually the 33rd District for State Senate. My apologizes to Rep. Frank Dermody for accusing him of challenging someone petitions when he had nothing to do with it.
45th District: The petitions of Maribeth Taylor (Dem) are being challenged by Rep. Nick Kotik. Rep. Kotik has also done this before against the same candidate.