Tuesday, for the first time in its history, more Puerto Ricans favored becoming a state than maintaining the island's status quo as a U.S. Commonwealth. But put away the needle and thread for now — it'll likely be at least 2015 before America sews a 51st state onto its flag.Read the rest here.
Adding a state to the union is a fairly easy process, legally speaking. Article Four of the Constitution allows Congress to admit new states into the union with simple majority votes in both houses of Congress (and a Presidential signature). Puerto Rico is a United States territory without its own sovereignty, so technically Congress doesn't even need the island's approval.
It is worth noting that the referendum was very confusing. While a majority did vote to change the island's status fully a third of the voters did not bother to vote at all on the second part. So I am dubious about how strong the sentiment for statehood is. That said the purely partisan objections to admitting PR to the Union are offensive. If you want an taste of this see the commentary on this thread over at Free Republic. Warning FR is an extremist website and is emphatically NOT endorsed by A/O.