I think Fergie isn't handling the goalkeeper situation very well. I don't think I'm coming out with a groundbreaking opinion that no one else has had, but I was thinking about it, and I get the feeling he's trying to deal with the Lindegaard-De Gea 'rivalry' (or competition, whatever) as he would for a field player. Basically, I'm convinced that in his mind, SAF believes that putting them one against the other, forcing them to compete, dropping them after mistakes, is going to make them stronger and will benefit the team in the long run. I don't agree with him. I think Fergie doesn't quite grasp the specificities of being a goalkeeper (that's no slight on him, he's amazing on so many other points, I doubt it's blasphemy to point out some weaknesses) and this situation at the moment is just hurting De Gea (cos in any case, I doubt, whatever he says in interviews, that Lindegaard came believing he'd be n°1). I think the right thing to do would just be to stick De Gea in goal when fit for the major games (PL, competitive CL games) and use Lindegaard as a backup who plays cup competitions. Where you can get away with this type of rotation policy with most field players, it's really difficult for a goalkeeper due to the particular nature of the position which requires good reflexes with your defence, habits, communication, comprehension... things that come with long strings of games, confidence and so on.
I might be wrong, I hope so in any case, but I really don't think this constant dallying with the GK position is doing us any favours at the moment.