Tried it out and -- Long story short -- works as advertised. A workable solution to the "book cover" feature.
My Notes (for what they're worth):
Spoiler:
Install instructions were clear and thorough. Config parameters a little confusing -- creating a form or default buttons would help (I know, easier said than done).
Scheme works best if "calibre_cover" is the only cover marked for standby. Suggest a note in part D.
Part D is a part of the setup, so suggest part D renamed to "Setup 'Copy Cover' on Reader" (or something similar).
Checking errors:
multiple books -- error trapped by plugin, message makes sense.
missing cover -- error trapped by plugin, message makes sense.
*Insufficient space -- error trapped, message makes sense.
*No books selected -- error trapped, message doesn't make sense:
ERROR: ERROR: Unhandled exception: <b>IndexError</b>:list index out of range
Traceback (most recent call last):
File "<string>", line 93, in copy_cover
IndexError: list index out of range
I'm out of errors. Calibre hasn't crashed in XP and it works on my -350.
The two *'ed errors were trapped by Calibre, not your code. Should be fine, but these may need further testing cross-platform.
All together, it looks like you've got a clean Beta!