Thank you so much for this! I've been less than impressed with my Kindle PW in the first place (pink/green blotches across the screen, both in my original and in my first replacement; I'm waiting for replacement #2), but not having my custom screensavers made it doubly tough.
Your little Python script really does the job with Covers. I used to create my own screensaver of the book jacket for each title I was reading and rotate them in -- but this is so much simpler. Thank you again!
Any chance the font hack is on your radar screen? I do miss my Georgia font (don't know why it's included in the Kindle iPhone app, but not in the Kindle itself...)