We'll have more details tomorrow but, for now, Tim Montgomerie has the lowdown. As I said a few days ago, this is a smart move from the Tories, and gives them a good message to deploy on the doorsteps. Indeed, Tim has already drafted it for them: "Seven out of ten working people will be better off if Cameron becomes Prime Minister."
UPDATE: The Telegraph has more information here. Looks as though the Tories might keep the rise for those above a certain income (the Telegraph speculates £37,400). Either way, we'll know for sure tomorrow morning.