In a split decision, the Pennsylvania Supreme Court ruled that the state's Congressional Redistricting Act of 2011 violates the state's Constitution, ordering the General Assembly to submit a revised plan to the governor by February 9th. Failing that, or if the governor doesn't approve the plan submitted, the Court will develop a plan for redistricting. The Court further directed that the new districts will be effective for the May 15th primary. The changes will not affect the March 13th special election in the 18th congressional district.
The decision is being appealed to the U.S. Supreme Court, according to this AP article. Providing some background, the article states that "Republicans who controlled the Legislature and governor’s office following the 2010 census broke decades of geographical precedent when redrawing the map...they shifted whole counties and cities into different districts in an effort to protect a Republican advantage in the congressional delegation. They succeeded, securing 13 of 18 seats in a state where registered Democratic voters outnumber Republicans 5 to 4."
Here's a map of the current district boundaries for the entire state, colored by party of the current incumbent, with the 18th currently vacant (was Republican-held).
This 2nd map is the Southeastern corner of the state, the districts in and around Philadelphia. This is where some of the worst gerrymandering took place. District 7 (shown in tan) is sometimes referred to as "Goofy Kicking Donald Duck"; it is one of the most oddly-shaped districts in the country.
Any approved redrawing of the lines will almost certainly benefit Democrats in November. In an already very competitive year, this will provide additional opportunities for that party to gain the 24 seats they will need to take control of the U.S. House.