I'm not a birther and I don't think being born in Puerto Rico disqualifies you either (as someone else noted, Barry Goldwater was born in Arizona territory to U.S. citizen parents). However, people are forgetting the other part of the constitutional requirements for presidency, residency. It makes it very clear: "No Person except a natural born Citizen, or a Citizen of the United States, at the time of the Adoption of this Constitution, shall be eligible to the Office of President; neither shall any person be eligible to that Office who shall not have attained to the Age of thirty five Years, and been fourteen Years a Resident within the United States .
Even if you assumed they meant "non-consecutive" residency within the U.S., if you add up Fortuno's years in Washington when he served in Congress and his years in law school, it STILL doesn't add up to 14 years. I can't imagine the founders meant that living on an island territory somewhere "counted" as "within the United States", or the entire clause would be pointless since people nowhere near the United States could claim to be "residents". I think they put that clause in specifically to prevent what Fortuno advocates want here... someone who was "American born" on paper but has no ties to the United States physically or culturally in many years suddenly becoming the leader of our country. The clause was inserted for good reason, to prevent such a bizarre thing from happening.
As someone else noted, it sounds like a bad Twilight Zone episode (Rod Serling intoning: "Meet Luis Fortuño, age 51. He's the leader of a small spanish-speaking Latin American island who is about to become President of the United States. Not possible in the real world, you say, but Sr. Fortuño is about to find that anything can happen... in The Twilight Zone.") 