Gustavo Madero, campaigning to be César Nava's replacement, says that there will be no PAN-PRD alliances in 2012.
That makes sense. I've heard people talk about an alliance for the presidency in 2012, and I'd say that misreads the situation. Even at their most cynical, these were tactical, short-term agreements meant to stem the PRI tide, not a merger. (And in Puebla and Oaxaca, they could plausibly be seen as a common front against authoritarianism.) The PAN and the PRD both recognize that it is in their mutual best interest to slow the PRI's momentum well in advance of 2012. The ultimate goal of the alliance for both members isn't a PRI loss in 2012 by any means necessary, but rather a potential win for the respective party, a precondition for which is weakening of the PRI, at least in their view. The final piece of the alliance puzzle is the state of Mexico, not the presidency.