Downloaded and installed 0.7.904 and it's working smoothly. The cover art is now being transferred when books are copied over to another library.
Just want to mention I noticed what is perhaps an interface issue. I don't know if it is a beta issue or something that existed before. I only noticed it today when using the beta. For books with really long text in a custom long-text field, when you click on that book in the Book Details pane, the window that opens is larger than my PC screen and so the top title bar gets cut off. I also can't move the window. To exit the window, I have to hit the escape key. I'm using a netbook now so the screen is only 1024 x 600, but even when I change the resolution to 1024 x 768 it happens. One can replicate the issue by pasting any long piece of text into a custom long-text field and then clicking on that particular book in the book details pane.
I guess two ways to fix it would be to either exclude custom long-text data from showing up in the book details window OR limit the absolute size of the book details window and have any long-text data appear in scrollable inset windows. I have no preference as I never really use the book details browser window. I just thought you should know about it as it could impact others who use long-text fields like I do.
I'm using Calibre on Windows XP SP3 and connect to a Touch 3G with Stanza.
Thanks to all who have been working on Calibre. It's progressed so rapidly. The new tweak epub feature is wonderful!