In a press release issued by Reid's office this morning, he cites "legitimate issues" brought up by protesters keeping the bill from being voted on, and calls on PIPA author and Vermont Senator Patrick Leahy to "continue engaging with all stakeholders to forge a balance between protecting Americans' intellectual property, and maintaining openness and innovation on the internet."
Reid remains "optimistic" that the Senate will work out any issues with the bill "in the coming weeks," but given the bill's sister act in the house (SOPA) also getting a big delay, we're not similarly optimistic about PIPA's reintroduction. Additionally, Reuters reports that a "senior Democratic aide" speaking on condition of anonymity claimed the act was unable to garner support among the Senate, thus abetting in this delay.
Update: House Judiciary Committee Chairman Lamar Smith (R-TX) issued a statement in response to the PIPA announcement, specifically addressing his SOPA bill in the House. "It is clear that we need to revisit the approach on how best to address the problem of foreign thieves that steal and sell American inventions and products." His complete statement can be found here.