Apparently a hamstring was giving him problems as well. Explains inability to push down on some shots, movement and serve.
Andy said he picked this injury up during the Fed match. Nothing too serious but it made his leg feel 'tight'. Actually between this and the blisters it was truly amazing that Andy was able to move around the court and even serve as well as he did.
As for the feather - I don't think Andy removing it was the problem but the fact that, as he said later, he thought about whether he should do so or not, so it seems to me that it was the thinking rather than taking spontaneous action which did the damage. Oddly enough it was a white feather, considered by many to be a sign of cowardice, but there was nothing in the least cowardly about Andy's performance.
As for the heckler - I'm not sure what powers umpires have in these situations. Can they order a spectator to be removed by security guards even if it means holding up play for a few minutes? If they can then this one was pretty negligent. If they can't then surely the security people themselves should have taken the law into their own hands and ejected him from the arena? From what I saw there seemed to be plenty of them around and so it should have been easy to identify the culprit.