Coming into Sunday's oh-fer, Harper was hitting .304; however, his walk rate was adequate at best, and he'd managed just one extra-base hit for the spring. Considering Harper's struggles in limited exposure to Double-A last season, the move makes sense.
Harper will primarily handle center-field duties for AAA-Syracuse, tweets Adam Kilgore of the Washington Post, and play center for the Nats once he's called up. This means that Jayson Werth will remain in right field, and Michael Morse will stay in left (until 2013, when Morse will likely shift to first base). Rick Ankiel or Roger Bernadina will be the Nats' regular center fielder until Harper arrives.
Provided Harper adapts to the position while continuing to develop as a hitter, he'll be considered Washington's center fielder of the future. For now, though, the challenge is for Harper to handle Triple-A pitching despite being significantly younger than his peer group.
As for a possible call-up date, keep your eye on Memorial Day. That's around the deadline for super-two arbitration eligibility, something teams typically try to avoid with their top prospects.