I noticed that covers are much lower res now than they used to be. I have used Calibre to download The Economist over the past 18 months or so and covers used to be of a fairly high resolution - I could read the text on the cover on my PRS950. Now, over the past 4 weeks, the resolution of the cover is way lower.
I have not tried other magazines. So I am not even sure this is a Calibre issue. But I wish there was a way to return to the old, higher res covers.