Even those of us who have been following the discussions about SOPA and PIPA have been having a hard time figuring out some of the exact details. First, SOPA and PIPA are different bills and have different specific provisions. Second, SOPA has not yet made it out of the House committee and amendments are still being debated on it. Third, since the last time Congress met to discuss either bill and the opposition has been growing, bill sponsors have declared that they will remove some hotly contested provisions from the law, but we have yet to see updated texts of the bills.
For these reasons it is very difficult to say specifically what kind of liability you might have under a specific scenario such as this one, until either bill has a final version that can be deeply analyzed and comes up for votes in both houses of Congress (assuming that the growing opposition does not succeed in completely stopping or at least greatly altering both bills).