I'd like to see a new man given three seasons, with the only condition being continued qualification for the Champions League, before anyone even considers firing him. That's how long he should have to get the trophy ball rolling again.
It's not as long as Fergie got, true, but this is a different era and he'll be inheriting a successful team, not one that needs building.
It's certainly longer than almost any other big club would allow, but then Fergie is living proof that patience pays off. We mustn't underestimate how much of a hole is going to be left when the boss leaves, and can't expect the trophy train to trundle on uninterrupted. The new guy will need time. Whoever it is - even Moyes - you won't catch me calling for their head at least until a few seasons have passed.
Of course, it's probably all bullshit.