Of both the viability of the Iraqi armed forces, it's current government and in many respects the prospects for the Surge.
If the Iraqi army is able to retake Basra, secure the other restive cities and clear out the various independent groups that are exercising governmental authority, there is reason to hope that the national government in place may in due time be able rule their land.
If they fail, If they have to rely on US and UK forces to do their job, if it is air power and not their army that fights, it is a clear indicator that our surge in Iraq has been a waste of resources. We have spend five years building up the Iraqi armed forces and police, their performance in the field is a test of both their ability and our strategy.
Unless one of the major factions makes the decision to step back, and delay the final confrontation, we should know by the weekend just what the final grades are.