I think it was extremely harsh on Guzan for him to be dropped, I don't agree with that decision at all.
Now Shay hasn't done anything quite a glaring obvious as Guzan's mistake against City, but he is not a better keeper than Guzan by a long shot.
Shay just doesn't seem to have any presence in the net, he is sketchy when it comes to corners, he barely commands his area, he gets pushed around, and he doesn't impose himself on attacking players at all.
If I was Guzan i'd be seriously pissed off with Sherwood at the moment. Shay should have just had the cup run, with Sherwood having a word in Guzan's ear telling him to get over the mistake, step it up and if he doesn't he'll be dropped.