Some will start hiring in 2013. United and Delta most probably will. (Delta might ge some new planes, though, but not many. Not sure. American will start getting the new 300ER's too). All three expect attrition in numbers because of the mandatory age retirement of 65 however, from 2013-2023. So get started!
Pilots furloughed by United will be given first preference when offers go out. Get your green card before you apply. There's a seniority list on most legacy airlines (L-UAL and L-CAL pilots working on an integrated list as we speak).