Pennsylvania is the most populous state that does not have a law that says write-in candidates must file a write-in declaration of candidacy, if they want their write-ins tallied. Instead, all Pennsylvania write-ins are valid, and the law requires that they be tallied. But, even though most counties tally them, the state this year will not make any statewide tallies. By contrast, in November 2008, the state tallied the write-ins for Ron Paul (3,849) and Chuck Baldwin (1,092).
The Pennsylvania Bureau of Elections says anyone is free to come to their office in Harrisburg and look at the county returns and compile statewide returns. The state also says that there are a total of 11,630 presidential write-ins from November 2012. The only presidential candidate who were not on the ballot in Pennsylvania, but who received at least 50,000 votes nationwide, are Virgil Goode and Roseanne Barr, so chances are each of them received a few hundred. But no one will ever know that, unless someone goes to the Harrisburg office and looks.