That's so cool! I don't know if I'm ready to muck with my own firmware just yet, but I think it's a great idea to hack it. Keep Amazon on their toes!
That said, though the Chinese text is beautiful (and I love their menus and stuff), the mono-spaced English font (in post #33 of the thread) causes blood to pour out of my eyes... Kerning is not optional, it's the life blood of good-looking Western text.
The PDF font darkening is something I've wanted ever since I started putting my own scanned-and-PDF'ed books onto my K2i. They all display very washed out on the e-ink screen and I haven't figured out just how to massage them to display better (in Photoshop before I combine the individual page images as PDF). I have lots of these scans though, so having an on-board PDF darkener would be a godsend to me.
I'll be keeping an eye on this!