One piece of information for those with Waterstones Kindle.
I bought a Waterstones Kindle in December (as many others I didn't want to wait to get it from Amazon directly), but I was very disappointed to see there is only the Waterstones screensaver on it (from the moment I bought it).
Today I tried the screensaver hack with no luck. Afterwards I decided to reset the Kindle (not reboot, reset), which removes all files from Kindle. The Waterstones screensaver is gone now and I see the default Amazon screensavers instead. So for those who want to get rid of the Waterstones screensaver, try reset first.
I'm going now to try the hack, but this is already a progress! (The Waterstones screensaver was driving me crazy!)