Well, that came out of nowhere. The Syracuse Orange and Pittsburgh Panthers were announced in a Sunday morning release as the ACC's 13th and 14th teams. Pretty amazing, considering that before Saturday there were barely even rumors of these schools getting the call-up.
There's no reason to assume the ACC is done, as it could still lose Virginia Tech to the SEC, somehow convince Texas to join or wait and see if there are any other suitable Big East leftovers once that conference collapses. The Big East's bylaws place Pitt and Cuse into the ACC in 2014, but the Big East isn't really in a position to enforce much of anything, so presume 2012.
The rationale for the additions, from commissioner John Swofford:
"The ACC has enjoyed a rich tradition by balancing academics and athletics and the addition of Pitt and Syracuse further strengthens the ACC culture in this regard," said commissioner John Swofford. "Pittsburgh and Syracuse also serve to enhance the ACC’s reach into the states of New York and Pennsylvania and geographically bridges our footprint between Maryland and Massachusetts. With the addition of Pitt and Syracuse, the ACC will cover virtually the entire Eastern Seaboard of the United States."