Ha! Nice find!
And the screensaver stuff is in there as far back as in a Kindle 2 (at least on 2.5.x)!
It automatically tag them with the 'Slide and release power switch to wake' black bar on the bottom (at least on a K2).
Couldn't get the framework to pick up a config file from /mnt/us/system instead of /var/local/java/prefs though (just in case it might be doable *without* a jailbreak, like the alt font family).