From Nate Silver at the NYT:
Georgia rules require that a candidate get at least 20 percent of the vote statewide to get proportional delegates there. (The candidate is still eligible for Congressional district delegates even if he does not meet this threshold.)
Exit polls project that this could be a close call for Mr. Santorum; they had him tracking to almost exactly 20 percent of the vote in Georgia. He is doing slightly better than that in the actual vote count so far, with 26 percent of the vote, but most of the few precincts that have reported so far are from south and central Georgia and are likely to be stronger for Mr. Santorum than the Atlanta area.